Mailbox.org beta offers regular 2FA setup via authenticator. I’ve been using it for months and I’m yet to run into any issues.

In general, I’ve been with MBO for almost a year and I’m happy with the service. You basically get a complete replacement for the google suite which you can use via your app(s) of choice.

1.111B class .xyz domain costs some 1 EUR per year. You’re limited to <6-9 digits>.xyz format (e.g. 012345.xyz) but if that doesn’t matter for your use case then this is the cheapest solution. You can get these via Porkbun, etc.