Makemkv tries to open a file in $SNAP with mask 'c'

It’s super weird to write to /usr/share but I would have the following-advice. Use a layout for to bind-file $SNAP/usr/share/MakeMKV/appdata.tar to $SNAP_DATA/appdata.tar.

You would also have to ship the vanilla appdata.tar somewhere in the snap and use the install-hook to copy it to $SNAP_DATA