Github dislikes email “aliases” so much that they will shadow ban your otherwise normal activities for months, and once flagged, support will request not only a “valid” email domain but also that you remove the “alias” email from the account completely.
Federated Git has been a thing ever since git was conceived:
They mean like I want to be able to open an issue on your instance using an account on my instance. Forjero is working in this