I used to get email for an org that had a similar domain as me (they had an extra letter in the middle). Thankfully, not a very big org, I would just bounce addresses that got a lot of misdirected email and I think they shut down and that really solved the problem.

Still annoying, but not as bad as gmail. I just got an email, in Italian, about someone adding a passkey to their ebay account. No way to tell ebay it's not their address / it's not my account.

That is that we do as well, but she still has her own email account that I presume she'll keep as long as Gmail exists.

I've noticed a lot of sites and orgs wont accept email domains that aren't gmail, hotmail, outlook, icloud, or yahoo.

Interesting. I've used my personal domain name for email for almost 30 years and I've never had that problem.

It's a tactic to prevent burner/spam accounts created using temporary emails

Similar boat (~25 years) and, while I've run into some sites/services that rejected my domain, I'm pretty sure it's happened fewer than 5 times, total.