If you got MakeMKV via Flatpak, you may want to get Flatseal, and manage permissions. It may not have access to that device.

sudo modprobe sg made MakeMKV detect my portable Blu-ray optical drive on my Steam Deck

Is it a permissions issue? If you're running software through flatpak, do you need to enable access to the optical drive device through flatseal?

Are you able to playback DVDs through VLC?

On my computer, I'm able to first run lsdvd and then rip the DVD to an ISO file using dd. If I don't run lsdvd first, dd fails.

Granted, I'm not using an immutable OS.

You might just need a DVD drive, but are using a CD drive. They look almost identical, but are different types of disc. Fortunately, DVD drives can use CDs just fine so you wouldn't have to juggle the two.

If you didn't grow up with optical media this would be a very easy mistake to make (I've even seen millennials and gen x mix them up). If you want to cover all your bases, a blue ray drive would be the thing to get but I'm not sure offhand about Linux compatibility. Probably fine though.

This is a dumb question, but is your optical drive only a CD drive, or does it support DVDs?