www.makemkv.com

Holy crap!

I know this is anecdotal evidence and isn't proof of anything, but I post this in case it helps someone else.

I bought Avengers Endgame UHD right when it came out. It never successfully ripped. I can play the disc on a standalone player. Yes, makemkv could open it and start ripping ...

Have you tried opening makemkv as administrator?