I was on gmail since the invitation too. Using their domain.

I started to use my own domain within Gmail 2 years ago. Transitioned things I cared about to use that email at that time.

Then this years I moved to Proton using that domain. And I'm forwarding Gmail to proton indefinitely.

I told my family, friends to start using that address going forward.

Slowly but surely as I get email into my gmail folder on proton I take the time to go change the address.

The big change is using an address from you own domain.