www.makemkv.com

What is the "tell" that indicates that these discs aren't encrypted so I can check in the future?

My trouble is with S04 Disc 3 it won't rip to an MKV with the same cannot decrypt problem others have mentioned.

If I backup without decryption can I then convert it to an MKV from there?

That's good to know! This is the file name: MKB20_v77_Dune-_Part_Two_1B3E

Dune 2 won't rip "The volume key is unknown for this disc - video can't be decrypted"