I've thought about using Github and using Github Actions to roll up different people's GH accounts' data into a "central ledger" but yeah, this isn't immutable and Github Actions keeps going down lol.

Twitter is a no-go since their API changes fairly frequently and I still feel burned from their API rug pull a decade ago.

That’s actually the only reason it’s usable for this. Because you can’t use a public database for anything at all once it’s full of spam and CSAM; not only will it get blocked but nobody will work on maintaining it.