Hi @jlskuz , yes, of course you can use the icons I designed. I'll check out the HIG guidelines and see how I can request the git merge (I don't know how to do this).
I would then only finish off the icons to comply to the HIG and remove the mouse cursor.

I also agree with @colomar
In any case, just to keep in mind the current official status of document format handlers in okular:
https://okular.kde.org/formats.php

Usually I fill in very simple PDF's forms and annotate pdf with okular. I also exchange them with colleges and secretaries at the institute where I work. They work mostly with Win and to a lesser extend with mac. So far I have had very few problems in terms of rendering the information or the annotations, really very few. However, it might be due to the kind of very simple forms and annotations I'm processing in Okular.

Just in case that something happens here it is the original svg of the proposal. It is just the design without the application examples.

I agree with ngraham it would be nice if KDE somehow can address to those academics in the humanities and social science institutes. Word processor, slide presentations, and a reference manager (e.g. Zotero) are the main tools used here. As many her know right now MS office provides the common tools for that purpose, even when the interfaces are not friendly. It is a matter of custom and market pressure. I think in this regard KDE could collaborate with the document foundation to strengthen the integration of Libre Office and the desktop, along with what it is mentioned as campaigning the use of KDE at academic conferences in the humanities and social sciences. University and city libraries is another place to go bc usually fresh-students get their introduction to those tools in those places.

@alcinos

ripple vs trim For trimming, I think we would need left and right trimming cursors.

I've added an indicator the the edge of the clip. It is cyan to differentiate of the or the ones used for advance trimming operations (ripple, slip, etc )
I also created a cursor for that that is different for the ripple. I think with one cursor is enough. This one is also a simplified version of the ripple cursor.
All indicators and cursors for advance trimming ops use a combination of arrow and bracket-like elements whereas trimming uses a combination of arrow and a simple centred bar.
What do you think?
I change colours to one plain fill colour without stroke.

Ohh I forgot to add the link for the Davinci Resolve example of trimming.
https://www.premiumbeat.com/blog/dynamic-trim-tool-resolve/
As far as I've gathered Avid don't use colour to indicate trimming operations and Lightworks uses red and blue to indicate in and out over a light green timeline.

Thanks for the feedback alcinos.
I integrated the icon to the toolbar in a light and a dark theme.
I also added the mouse cursors for each of the trimming operations.
I did again the indicators, removed the arrows, and thinned the actual in and out indicators. After further consideration, they looked too thick for me. I changed the colour of the indicators to green, because in the current interface once a clip is selected in red and green provides the strongest contrast to red.
I've observed something very interesting in the interface of Davinci Resolve NLE. It adds a rectangle to indicate the hidden-actual length of the clip been rippled, slide, slipped, or slide. This informs visually the user the limits for the trimming operations on the footage. I think adding something like that would be a nice idea for the UX in kdenlive. Using the red colour, already indicating the selected clip, I added a ⎵ on the bottom of the clip to indicate the total available length of the clip.
To illustrate how this would work I add to simple animated gifs. The Slide gif is not exactly as the operation but it shows that in that case the bottom indicator stays while the clip slides with the in and out green indicators. That is the opposite case by slip, the green indicators stay and the bottom indicator shows the amount of slipping.

I've sketched a simple proposal for the icon set for the trimming operations. I followed the style that Kdenlive already has. I based the icon set on the arrow already in use for Inserting clip zone in the timeline. The proposal includes the grid for generating the set. I also include examples of how the icon set looks using three different desktop themes, their posible location and drop down on the toolbar, and finally a first sketch for the timeline selectors.