Check compatibility for all your programs before you move. Most Linux programs work on Windows but not vice versa. If you’re not in a rush, try switching to programs that have a Linux equivalent before you move so that you’ll have less of a culture shock. If you need any killer apps that don’t have a Linux equivalent you’re going to have to make your peace with that ahead of time, otherwise you’re just going to end up switching back.
KDE is a good choice, and Kubuntu should serve you fine; if you end up going with Kubuntu, I would recommend sticking with it for at least half a year or so before considering switching to something else, as that will give you time to really understand what you like and don’t like about how Kubuntu and KDE work.
Oh my gosh, I was just experiencing the PWA rotating thing and it was driving me nuts trying to figure out how to stop it. Nothing else on my Android auto-rotates, and I didn’t immediately see any settings that could stop it. It seems like all PWAs created from Chromium (Vanadium to me) do this on my phone. I created the PWA from my Firefox app (Ironfox to me) and it seems to work fine, though it uses my installed Firefox extensions on the PWA - notably I have uBlock Origin set to block images above 50kB until I click them, which I have mixed feelings about using in conjunction with PieFed.