Had to scroll down this far just to get to markdown files. Although I write with a bit of a delay. Once I get something working. Then I document what worked and what didn't. Alternative methods and issues I had with the alternatives.
D_Air1
So something disabled your monitors and you were able to get them back by quickly enabling them during the brief period of time that they were visible. The monitors should still be listed in the display configuration even if disabled. May be worth filing a bug with kde. Seems like a massive oversight if that isn't the intended behavior.
My brother used to use enterprise windows 10 until he started having that vary issue with trying to play COD.
It certainly isn't a permission issue like others are claiming at least for the window rules. It could be a bug, but as far as I know the steam deck does not use the latest version of kde, so it may already be fixed and isn't worth reporting.
As for onlyoffice, if I had to guess. It is forcing its own window decorations and therefore you don't get all of the same options as with windows that use the breeze decorations from kde. However you can still create window rules for these window. If I recall correctly. The default shortcut is alt + F3 which should work regardless of which decoration the window is using.
What does the kwin rule for evolution look like?
Lastly, the password thing is the only one that could be related to a permission issue. I however don't believe you should start mixing keyrings. kwallet is probably already installed and running. Like I replied to one other person already. Both gnome-keyring and kwallet use the secret service standard. The only reason it could not work is if evolution hardcoded gnome keyring instead of relying more generally on secret service. However, I doubt that. You could even use keepassxc as a secret service provider if you wanted to. Although it is a bit more annoying in practice.
We're basically already there. KDE has already moved to the secret service standard that is used by gnome keyring. The real issue in my experience has been applications hard coding a dependency on gnome-keyring and not secret service. Some applications such as mailpring have fixed that hard coded issue, but it is still an issue in other applications.
Honestly, it seems pretty similar to cockpit which should be available in most distros repos.
The reason most distros don't do this is because they usually try to steer users to their preferred desktop. I don't mean that in a bad way, but often they call it the flagship edition. This is usually the desktop environment that they develop and test. Think Linux Mint with Cinnamon, popOS with Cosmic, Zorin, etc. Pretty much every other distro that has options do exactly what you are showing through the use of the venerable calamares installer that you see in your screenshot.
Somewhere between $10 and $50 per transaction. Its not every month, but just randomly throughout the year depending on what I have.
Dolphin should be qt6 for quite some time now. So you should need qt6ct. Also I'm not sure if either qt5ct or qt6ct is maintained. Their is a fork in the aur that I have been using https://aur.archlinux.org/packages/qt6ct-kde, but not sure what to do outside of arch.
I will use old machine until the damn thing quits on me and be happy.

I've used rustdesk off and on. It is pretty good. I use it to help my aunt with "computer stuff".