This is one shortcoming of having your own domain. If you let it expire, there is nothing preventing someone else from recycling email addresses.
On the other hand, having your own domain gives you many advantages, including not having to fear that you'll lose your email address because a big tech company decides to ban you for no reason (which is tangentially related to what happened to OP).
So, it's a bit of a double edged sword, but can be good as long as you are diligent about renewing your domain.
Thankfully, with cloudflare offering 10 year renewal terms, things are much better these days. You could bet prices fall and go year by year but given inflationary pressures, it almost certainly seems to be a good deal to do a 1
So transfer it to another registrar. I registered one of my primary domains through them way back when they started offering G Suite for free, but after a year I moved it to the registrar that holds my other domains. It's not difficult.
On the other hand, having your own domain gives you many advantages, including not having to fear that you'll lose your email address because a big tech company decides to ban you for no reason (which is tangentially related to what happened to OP).
So, it's a bit of a double edged sword, but can be good as long as you are diligent about renewing your domain.