I'd venture a guess it's never been about security. Microsoft easily maintains their own products FTAs but will not preserve settings supporting other vendors Had they simply respected things like user choices of Adobe Acrobat, etc., Photo Editor, Music and Video player with Win11 they would...
Looks like that UCPD is overridden by a new upgrade to Windows 11 that blocks programmatic FTA changes, called "User Choice Latest"
UserChoiceLatest – Microsoft’s new protection for file type associations – the kolbicz blog