I went with 11 for the aforementioned issues. Originally wasn't planning on it, but when I saw that 10 wasn't supported, and that there were performance concerns with it, I bit the bullet and installed 11. Have been pleasantly surprised by it. Followed the FW guide for upgrading the main board (from my 11th gen), and it went pretty smoothly. No online account needed either (use Rufus to make the boot media and remove that requirement). I may even change my desktop machine over to it.
Incidentally, Stacksocial has Win 11 Pro right now for $25. Cheapest you'll find it anywhere.
It definitely sounds like a backlight issue, but check the display connector again. I had some weird video problems with my AMD main board when I upgraded, some of which sound a bit like yours. It ended up being a speck of dust or something in the connector. Once I blew that out with some canned air and reseated the connector, everything worked properly. Worth a shot at least.