shelltile VS PaperWM

Did you try the shelltile extension?

About the tiling there are extensions that alleviate some of the issues that GNOME's default tiling has. WinTile is one that adds 4 corner tiling just like Windows 10, (although I had some problems with snapping in/out the top panel and ended up not using it. Perhaps one day native 4 corner tiling will be implemented). ShellTile, gTile, PaperWM and the Pop shell are some extensions that give GNOME some advanced tiling capabilities. I personally don't use them as I'm happy with the default stacking GNOME workflow and prefer to use a standalone Tiling WM like sway if I need to, but I see the value in having a Tiling WM in GNOME and these are some of the extensions I've heard the most positive things.

Shelltile is another one: https://github.com/emasab/shelltile

But with auto-tiling you need to place windows according to a pre-set configuration, it needs to fit whatever layout you want to go for and it needs to be able to resize the window without breaking the content. This works pretty well for libadwaita apps, but a lot of webapps seem to assume a certain minimum window size. Another issue is how to handle modal dialogues, where paperwm for example sets an override to ensure they're not attached to the main window. Should the settings window then be treated as a separate window and tiled, or should it be left floating above all others?

I like Gnome's simplicity, agree with most of its deviations from the tired old Windowsy desktop status quo, and am very happy to depend on all its great integration work. I can't quite live with the simplistic window management, but extensions cover that (as they do much else). With Fedora + Gnome + PaperWM, I'm quite at peace with the current linux desktop situation.

Still I'm looking forward for something like PaperWM to be possible in KDE - or even to write it by myself

I have noticed in one of your comments in this thread that you are looking for novel ideas of the UI look. As others commenters stated, you might be interested in tiling window managers like i3 [0] or sway [1]. They are truly a gem for productivity and sometimes for an eye [2].

However, I love the concept of scrollable window manager like PaperWM [3] is. When I had a smaller screen (24" 16:9) I was complaining a lot on unused space on my screen. With PaperWM I was finally happy with its dimensions, because I could have huge IDE on the left and small part of terminal displayed on the right. That way I knew if something was printed to terminal, while my editor took 80% of the screen.

[0]: https://i3wm.org/

[1]: https://swaywm.org/

[2]: https://www.reddit.com/r/unixporn/

[3]: https://github.com/paperwm/PaperWM

If you want something really different, give PaperWM a shot.

You may want to try PaperWM (GNOME extension) https://github.com/paperwm/PaperWM