For what it's worth: I self-host gitea, and it gives me the possibility to import not only repos but also issues, projects, etc from GitHub, gitlab, bit bucket, and a handful of others.
I don't know if Utterances can work with gitea's API. If it does, then in theory you should be able to migrate to gitea from GitHub for this use case.
As long as i can prompt-engineer my way into twice the salary for half the hours, that might still be worth it!