I just want to say how pleased I was to have a surprisingly smooth install experience. I'm running ubuntu 20.04 x64 headless with the 5.13.19-051319-generic kernel and the make install experience went smooth as butter. It's worth noting that the "OPTIONAL: Building with latest libavcodec" section isn't necessary with modern linux releases. I'm using the Pioneer Electronics BDR-XD07UHD which also worked straight out of the box with no flashing needed.
I did have a bit of a time figuring out that the makemkvcon man page literally meant use disc:0 nomenclature; I kept on trying with /dev/sr0 and thought something was wrong.
Anyway, thanks!