Finally got around to trying this and YES it works.
You don't need to turn of the Ransomware Protection completely. You can use the option to allow all the MAKEMKV exe files through controlled folder access.
Makes you wonder why MS is blocking this in the first place. Maybe it's the decryption algorithms it doesn't like but none of my other AV/Malware programs seem to object to it.
I just upgraded from Win 10 Home to Pro and I was experiencing the same issue. Try this on top of allowing the app through your security program and reinstalling MakeMKV. Find the makemkv.exe file and right click on it. Check the "run as administrator" and hit apply.
Screen Shot 2021-04-18 at 11.32.43 AM.png (837.83 KiB) Viewed 8735 times
Dude, this totally helped me out. I wasn't sure that with my hardware changes, and moving a 5.5" drive from a desktop to a USB controller on a laptop would work. I was able to browse the drive through the Open File dialogue, but it would not populate automatically. I get the annoying UAC prompt because I am running in admin mode, but that is better than before.