There is an issue for it, but it doesn't seem that it is being worked on at the moment

https://github.com/aeharding/voyager/issues/9

PRs welcome. Unfortunately Lemmy's spoiler markup is bespoke

Seconding this one. Not that I care that much about spoilers myself, I know some people do and I'd hate to wreck their experience because I can't even verify whether my own spoiler tags worked.