I have self-hosted both, although admittedly Gitlab was quite a few years ago. Forgejo is faster and lighter, GitLab is slow and huge. Unless you know you need a very specific GitLab feature, I’d go Forgejo all day.

I bought the whole Steam deck, I’m gonna use the whole Steam Deck!

Just following your above link, you could pre-convert your comics using this: https://framagit.org/nicooo/kumiko