I like Flatpaks, but Mint really needs to do a better job of communicating when you should use it over debs. And also deduplicate things so the deb and flatpak don’t both appear in the list. When I was looking at the software centre thingie, my first thought was “wow this would be very confusing for a new user”.
Hidpi and waking from suspend have pretty much (as I understand it) always been problematic on Linux, especially on Nvidia. It’s getting better, but Nvidia isn’t really keen on working with open source stuff.
If you do go back to Windows, I would ask that you be open to the idea of trying it again in the future. A lot of the issues you are facing are being actively worked on, and a lot can change in a year or two.