If you own your own domain, you just switch email providers and redirect your domain to them, and that's it. No changing accounts everywhere, telling friends to change, etc.
Yes, a royal pain in the ass. However. I did it recently but the way I did it means any future moves, of all my 300+ websites that I have logins for, is now done in seconds.
I signed up for SimpleLogin and a custom domain. I then went around creating aliases for all these sites. Changing the sites is indeed the worst part. Still, this is the last time I will ever do it. All my aliases were pointing to my Gmail account. Once I'd finished I settled on Proton. I just moved all my aliases to my Proton email address.
No one knows my Proton email address other than SimpleLogin.
I haven't yet, but I can now ditch Gmail. I still keep the account for a number of reasons but none are for emails.
I've also been testing Tutamail. I can get aliases to go to multiple mailboxes. I have the ability to respond to the emails from either Tuta or Proton and the recipient is none the wiser of where my mailbox resides.
It certainly can be a bit involved. When I moved from Gmail address to my own personal domain I did it slowly over a few months.
I set my Gmail address to automatically forward to my new email address. Then I setup a quick filter which added a label on everything that had been forwarded. Once a week or so I would look at all the emails that had been forwarded and update them to my new email (or delete them if unwanted).
My only criteria when switching email was to be able to use my own domain name. Now I almost don't receive anything on my gmail and I can transparently switch provider. I think it was a relevant move, I won't move to self hosting but I could ! :)