Yeah, this. Remark, the markdown library Voyager uses, is very powerful but also extremely complex (it has to be, to deal with Markdown edge cases).

I made a bit of progress last week on a custom plugin but it’s a lot of work. There’s like 4 layers of parsing required.

I wish Lemmy used GFM spoilers, which just uses normal details and summary html tags. But alas.

It’s really annoying there’s no standard markdown syntax in common mark.

A quick Google suggests you're correct - big sites have implemented their own versions, but it looks like everyone has spent the last decade arguing with other about a CommonMark standard.