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.
I think Google Voice still gives out a free phone number as long as you tie it to your actual phone number. I used it for Craigslist all the time years ago to avoid giving out my actual number
A lot of services like PayPal will block known Google Voice numbers. Screw all these service for even asking. I can do 2FA without a phone so you must be trying to collect more data than you should.