Kind of a shame that this extensive write-up has sat around for 2 months with no comments, but unfortunately, I don't have much to add. I don't really use virtual desktops or activities much and haven't seen a great need to, so it's hard for me to really see how they should work. I have tried them and they have been somewhat useful, but I never really stick with them. It's just easier for me to control everything with the task manager. I'm not saying your reasons for liking Virtual Desktops aren't valid, but perhaps one of the reasons why nothing moved forward is that a lot of people don't understand them, including KDE developers and designers like myself?

It's not that Virtual Desktops and Activities are not useful but they are just presented in a way that doesn't make obvious how to use them. I wrote some blog posts in Planet KDE years ago explaining (creative) way to use Activities. But in fact if you need to explain intended workflows with blog posts you have a UI/UX problem.

My mockup mentioned by OP is supposed to make more obvious how to use Activities but I know it wouldn't be enough. In the meanwhile, here there is what I copy-paste on social networks when someone asks how to use Activities:

• I have files and folders associated to each Activity and desktops set to Folder View to show them.
• different plasmoids on each Activity, in particular notes
• different panels on each Activity thanks to Latte Dock (I use it only and no native Plasma panels)
• I have different favourite apps on each Activity
• I take andvantage of "freezing" some apps when I stop an Activity. For example I usually have multiple Dolphin, Kate and Okular windows on many virtual desktops; I can stop the Activity and all apps are closed and if I restart the Activity I get those windows in the same position and with the same documents (Kate and Okular) and paths (Dolphin) as before
• I have a Firefox profile on each Activity with different favourites, history etc.
• I use pytivity to start apps when an Activity start
• again with pytivity I set an Activity that start/stop Docker when the Activity start/stop. I also have on that Activity a plasmoid that indicates Docker is running or not, running containers and available images.
• I use Plasma Vault with Activities to mount encrypted folders
• I have an Activity that start KDE Neon in a Docker container and show it in a full screen window. When I stop the Activity the container stop. It's better than Virtualbox for my use case
• a gaming Activity that stop messaging apps that are eventually running and restart them when the Activity stop

Personally I've had the same experience as Noah: I find it easier to manage my workspace with just the task manager and Alt+Tab and whenever I try out Activities or Virtual Desktops, I don't stick with them. This goes for other platforms too which also implement these features, FWIW.

Even though I don't use Activities, I feel like the concept makes sense and I can envision myself using them for "Work" and "Home" activities. Unfortunately I always get stuck on the fact that my email client (Thunderbird) and web browser (Firefox) can't have per-activity settings, so I don't have the ability to set up the Home activity with only my home email address in Thunderbird and no work-related tabs in Firefox.

@alex-l You said:

I have a Firefox profile on each Activity with different favourites, history etc.

How did you do that? Does it let you have different sets of tabs per activity too?

In T13582#244379, @ngraham wrote:

@alex-l You said:

I have a Firefox profile on each Activity with different favourites, history etc.

How did you do that? Does it let you have different sets of tabs per activity too?

Firefox can be launched with different profiles with a CLI argument. Different profiles also mean a different set of tabs is restored at startup, if you have that option enabled, and this is the main reason I do the following. Of course one can manually create a different .desktop launcher and pin it in the related Activity to launch Firefox with a specific profile.

I automated this with a simple script that is launched by my .desktop launcher for Firefox. This check if there is a folder named like current Activity ID in Firefox's profiles folder. If there is, it start Firefox using as profile the one contained by that folder. If there isn't, it creates one with current Activity ID as name and place in it some symlinks to my default Firefox profile folder (because I want history, fav etc to be shared, it's optional, but this introduces issues when I run multiple Firefox instanced with different profiles, but I'm OK with eventually keep one Firefox instance and close the others). Of course I have set this script as default browser so that when I click a URL in an app it starts Firefox in the current Activity with the right profile.

[EDIT: Please don't introduce something like this in Plasma, the right way to do this is using Plasma Browser Integration to replace Firefox built-in session restoring with one that is aware of current Activity and restore tabs associated with it]

The script is the following:

#!/bin/bash

# ~~~~~~~~~~~~~~~ F I R E F O X - A C T I V I T I E S ~~~~~~~~~~~~~~~~#


# This script start Firefox with different session (different set of
# restored tabs) according to current Plasma Activity.
#
# Usage: ff URL
# License: CC-00
# Author: alexl@disr.it


#~~~~~~~~~~~~~~~~~~~~~~~~ P A R A M E T E R S ~~~~~~~~~~~~~~~~~~~~~~~~#


# Firefox profiles folder:
profiles='.mozilla/firefox'

# Firefox execution command:
firefox='env MOZ_USE_XINPUT2=1 GTK_USE_PORTAL=1 firefox'

# Base profile folder:
base='4qst6lze.default' # <-- IMPORTANT: replace with yours


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ S T A R T ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#


# Get current Activity ID
current=`kactivities-cli --current-activity | cut -d' ' -f2`

# Check if there is a profile folder named with current Activity ID
if [[ -d "$HOME/$profiles/$current" ]]
then
    # YES - Check if there is an URL as argument
    if [ $# -eq 0 ]
    then
        # YES - Start Firefox
        $firefox --profile "$HOME/$profiles/$current"
    else
        $firefox --profile "$HOME/$profiles/$current" "$1"
    fi
else
    # NO - Move to the folder containing the profiles
    cd "$HOME/$profiles/"
    
    # Create the folder
    mkdir "$current"
    
    # Link all the files from base profile folder to the new one
    for i in "$HOME/$profiles/$base/*"
    do
        ln -s $i "$HOME/$profiles/$current/"
    done
    
    # Remove session files
    mv "$HOME/$profiles/$current/sessionstore.jsonlz4" "$HOME/$profiles/$current/sessionstore.jsonlz4.bak"
    mv "$HOME/$profiles/$current/sessionstore-backups" "$HOME/$profiles/$current/sessionstore-backups.bak"
    
    # Remove favorites and favicons database for compatibility,
    # they will be recreated from respective backup folders
    mv "$HOME/$profiles/$current/favicons.sqlite" "$HOME/$profiles/$current/favicons.sqlite.bak"
    mv "$HOME/$profiles/$current/places.sqlite" "$HOME/$profiles/$current/places.sqlite.bak"
    
    # Start Firefox
    if [ $# -eq 0 ]
    then
        $firefox --profile "$HOME/$profiles/$current"
    else
        $firefox --profile "$HOME/$profiles/$current" "$1"
    fi
fi

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ E N D ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#

Wow. Impressive.

This kind of leads me to what I consider the Achilles heel of activities: every individual app needs to be made activity-aware. That seems hard enough for KDE software over which we have total control, due to disagreements about the scope of what set of the app's settings should be activity-aware. But since 3rd-party apps don't support activities at all, the concept just breaks down if you want or need to use 3rd-party apps. :( 5 out of 11 of my pinned apps are non-KDE apps.

In T13582#244491, @ngraham wrote:

Wow. Impressive.

This kind of leads me to what I consider the Achilles heel of activities: every individual app needs to be made activity-aware. That seems hard enough for KDE software over which we have total control, due to disagreements about the scope of what set of the app's settings should be activity-aware. But since 3rd-party apps don't support activities at all, the concept just breaks down if you want or need to use 3rd-party apps. :( 5 out of 11 of my pinned apps are non-KDE apps.

Third party apps don't need to support Activities or anything Plasma-specific at all but just XSMP (X Session Management Protocol), that is what let Plasma restoring the session after the login. Actually, Plasma's implementation of XSMP treats each Activity as a single session, this is what powers Activities restoring feature. If an app restores its session after login it would do so also when activating the Activity it is in.

Firefox never supported XSMP and this is a shame. Mozilla doesn't care of Linux/Freedesktop at all. At least one of the KDE browsers (Konqueror, Rekonq and Qupzilla/Falkon) supported it though. It happened that when I had to switch to Firefox because WebKit is crap I wanted to keep the restoring capability.

XSMP of course is X-specific but AFAIK some are working on a Wayland extension for this. GNOME will support it and for sure Plasma too if it wants to keep restoring session at login.

Third party apps don't need to support Activities or anything Plasma-specific at all but just XSMP (X Session Management Protocol),

Gotcha. That's pretty clever.

Unfortunately the point still stands since tons of apps sadly don't support it. It's not just Firefox; Thunderbird, LibreOffice, and all Electron apps also don't seem to support it. I'm sure there are more too.

In T13582#244856, @ngraham wrote:

Third party apps don't need to support Activities or anything Plasma-specific at all but just XSMP (X Session Management Protocol),

Gotcha. That's pretty clever.

Unfortunately the point still stands since tons of apps sadly don't support it. It's not just Firefox; Thunderbird, LibreOffice, and all Electron apps also don't seem to support it. I'm sure there are more too.

And so? Plasma restores windows for every app and for some of them it restores their state (tabs, open documents etc). This is already very good. The lack of integration of the apps you mentioned is on a different level, they don't support color schemes, open/save file dialogs etc.

Also KDE already has most apps that can take advantage of session restoring, namely file managers, text editor, document viewers, web browsers and so on. LibreOffice doesn't even have tabs, right? And most Electron apps are small utilities so there is not even a state that makes sense to restore.

For reference xdg-session-management protocol is the work-in-progress replacement for XSMP in Wayland: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/18

So in future it should be possible to:

1. Implement xdg-session-management in Plasma and KDE applications to provide session restoring after login
2. Ensure session restoring works also when restarting an Activity
3. Ask to third party applications and frameworks to support it (Firefox, Chromium, Electron, VS Code and so on)

This makes me think that Activities could be renamed Sessions to advertise session restoring as the main feature since basically nobody knows that now on X11 restarting an Activity is like restoring a session after login.