How do you use email alias with Apple iOS Mail and Gmail?

I'm going to start a new thread, as there are answers out there about setting up a custom iMAP account. That's worked well for years, but next month Google is going to stop allowing "access from less secure apps," which is required to make the custom IMAP work.

So, I have two email aliases (one from the university that I graduated from and another from my professional society). I have used one of these as my personal email address for going on 20 years now, having the mail forwarded to a Gmail account. Without using the custom IMAP trick in iOS Mail, I cannot figure out how to send email with the alias appearing in the from and reply-to fields. Supposedly you can set it in the "Accounts and Imports" settings for "Send mail as" in the Google Mail settings; but this doesn't work for iOS Mail.

Does anyone have any ideas? I really don't want to have to switch to the google Mail app.

An alternative. I've never been able to figure out how to use aliases with ProtonMail. Does anyone know how to do that one?

thanks.