I moved my email to Fastmail over a year ago. I was able to do this easily because I used GSuite with a custom domain, so it was just a matter of updating MX records and moving my old mail.

But it doesn't have to be a huge chore even if you have an @gmail.com email address. You can register a domain, and sign up with Fastmail (or some other mail provider where you are actually the customer and not the product), and move things slowly. Set up forwarding from your GMail account to your Fastmail account. Start using the new email address for new accounts. Slowly start changing the email addresses on old accounts. You don't need to do it all at once; just maybe set aside 15 minutes a day, or maybe an hour on a weekend, and gradually change things. Focus on the important things first, like financial accounts. Eventually you'll stop getting email that you care about through the GMail address.

I'm now worried about my other Google-held data, like photos and documents. Some of them are backed up, but I still haven't made sure everything is.