Thanks for the tips, everyone, but I’m going to have to conclude there is something wrong with the drive. Regionset can’t read or set the region code. I’ll have to try a different device.

It says:

Playback failure: DVDRead could not read 1/4 blocks at 0x01

I did not know that existed. Thank you. I’ll try that when I get home from work.

I’m on cachyOS.