Maybe none of the platform themes will be needed. Qt has still QGnomePlatform which is now used in case of Gnome. The only problem now are missing icons (namely Adwaita icon theme). There is an ongoing discussion so probably we will be soon able to solve this problem by just using icons extension from Gnome runtime.

Well, it's not a fork, it was written from scratch. I think it has more functionality/stuff from gnome applied compared to the default gnome platform plugin in Qt, it even checks what color scheme should be used (working only with adwaita), tries to apply some font scaling etc. It also has native gtk dialogs because they were ported from Qt. But in the end it doesn't matter that much which one you pick.

Alternatives:

• version different releases per KF5 release (i.e. 5.33, 5.34) always with the latest stable Qt.
• stable/lts (with Qt LTS) + master (latest KF5+latest Qt)

So it's a fork from the functionality in Qt? Any pro/con?

It tries to read configuration from Gnome and apply it to Qt apps, also preferes adwaita-qt as theme by default. Other than that I guess is identical.

We need to figure it out with Wayland too.
Note that it's not about desktop files, it's about including it in the finish-args.

Where's qgnomeplatform? How is it different from upstream Qt?

https://bugreports.qt.io/browse/QTBUG-60108

Would you accept a simple Qt patch forcing apps to use flatpak platform plugin when we detect we are running in sandbox (same way I used in KNotifications)? I know I should try to upstream this as soon as possible, but with all the stuff around I'm trying contribute to it will take a while. I think this would be the easiest solution for now, better than modifying desktop files, because you can also run apps using "flatpak run app_name" or run an app through discover where it calls the binary directly and portals wouldn't be used at all.

Appstream metadata for runtimes and sdk has been pushed already.

pushed