When snapd 2.41 lands, which is due shortly, makemkv should finally work with strict confinement. To test you can update to snapd in the candidate channel and install the build of makemkv in the edge channel. You also need to connect the hardware-observe interface so that makemkv can see your DVD/Bluray drive:
sudo snap refresh --candidate core
sudo snap install --edge makemkv
sudo snap connect makemkv:hardware-observe
This is made possible by some extra confinement rules that I’ve added to snapd, which have finally filtered down into a public release. 