Forgejo, a Gitea fork that I use, has support for it according to the page you linked. But the FAQ for Forgejo mentions it's on the roadmap so not sure how complete ActivityPub support is in Forgejo either.

https://forgejo.org/faq/#is-there-a-roadmap-for-forgejo

I only use my Forgejo instance for myself currently so I haven't looked at the ActivityPub features of it before.