You could donate to https://opencollective.com/gitea but there is no way to earmark a donation for a specific purpose. Or you could donate to https://liberapay.com/fedeproxy/ and earmark the donation for the implementation of federation in Gitea (expenses can be audited later on).

That’s great. I was going to provide you all the places I know about that would be helpful. But I have to ask first on FedeProxy forum: https://forum.fedeproxy.eu/t/advancing-federation-in-gitea/240/7