Don’t hold your breath on Mastodon. It’s a beast. Ruby on Rails apps are pretty hard to support in general, but Mastodon takes it to new heights (also requiring Node.js, PostgreSQL and Redis). It’s basically impossible to support in the current Virtualmin Install Scripts model.
If and when we’ve got better support for Docker/Podman in Virtualmin, it might be feasible, if there is a well-maintained container installation of Mastodon.
PeerTube looks like a Node app, which is also notoriously hard to support. Again, probably needs to be a containerized installation that you proxy to.
So…for now, if they have a container-based install, you should just use it, and proxy to it in Virtualmin. If they don’t have a container-based install, Virtualmin can’t reasonably support it today, and will likely never support it (until their is a well-maintained container install for it, and we have container-based app support in Virtualmin).