Installing Fallout 4 broke other games
Follow-up: I gave up and punted. After trying upgrading to Windows 11, reinstalling DirectX 12, multiple version of drivers and validating OpenGL, none of which helped, I backed everything up and reinstalled Windows from scratch. This seems to have done the trick. Thank you to everyone! I really appreciate your suggestions. Plus now I know a lot more for next time. Yay?
And to anyone having the same issue who came here looking for help, sorry.
"I say we take off and nuke the entire site from orbit. It's the only way to be sure." - Ripley