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.
Are you using 2FA ? With some services (Not Discord but others) I found out that when 2FA is enabled I will not have to suffer endless amount of CAPTCHAs and what not.