The problem above was caused by something adding itself to the .exe Open With list, which nothing should do. It can cause problems system-wide. And it makes little sense for a media player to associated itself with the .exe filetype.
(It's possible Microsoft added some protections within Explorer itself to prevent this. In the past, it could make it almost impossible to launch any exe even via the Start Menu. I ran into it myself once.)
I doubt that going back to 11 will help, since the issue is something outside of Opus making incorrect changes to the .exe filetype, but let us know if you try that and find it does help; if so we can investigate why Opus 12 would be more sensitive to this than 11. The update to 12 would not have caused the registry change, either way; that is pure coincidence.
But you can probably also fix the problem by doing the same fix as before, deleting the registry entries above. If those entries keep being recreated by something, it should be taken up with the tool that is creating them.