I have a domain with one of the new TLD which I used for my emails.
Most services worked fine with it, but there were a few cases where my email was flagged as fraudulent and I had to call, explain it was legit and provide with another email.
There was one service I registered which explicitly said they oy accept gmail addresses.
Roughly one year ago I acquired a new domain using the .org extension, I am migrating my accounts to this one, and I havent had any problems so far.
So overall my conclusion is that most services are fine with custom emails, a few of them block based on TLD and an even smaller subset will allow only specific providers. Since I am moving alway from big corp, having a widely used TLD that seems to be accepted in most cases is my personal sweet spot.
Thats great, we should at least have the option like so many games do now, instead of going tge starfield route