The Windows auto-update will sometimes screw up the registry. Also updates to apps, especially browsers, will silently try to take ownership of extensions. My Chrome update last week decided it wanted to own “.pdf” which I despise as Acrobat Reader is the only correct way to work with them (despite the fact we cannot get rid of that stupid helper panel on the right).
I suspect it will get worse under Windows 11, although the UI is a little better.
That might be it. Brave is showing an install date of 11/1, which is definitely not the original date, and might be around the time the problem surfaced, so it may be an auto-update of that that caused the problem. If so, though, it’s odd, because the Windows dialog only lists Opera, and neither Brave nor Vivaldi.
However, Brave is the one I almost never use, so I’ll get rid of it. I do still very occasionally use Opera.