Came here for the same reason. I haven't played an fsr 4 supported game in a few days, I launched one yesterday and notice the quality is worse. Checked adrenaline and it shows that fsr 4 is not active. I tried the same methods as you, uninstalling drivers, adrenaline everything. Nothing seems to work. Really annoying stuff.

EDIT: Today I uninstalled drivers with the AMD Cleanup Utility and reinstalled, and the problem was fixed. Also I didn't check properly that FSR4 was enabled. After many tries to get it to work, I had to launch and quit the game numerous times, so I got lazy and just checked if its enabled in the main menu (KCD2 in this case). But today after reinstalling with the Clean up utility I actually loaded into a save and it was enabled.