Back to the original question there is another halfway domain and free email system that I have used for many things and I think works well. You can set up your own domain email addresses with some domain registrars (I use Porkbun) and then use their free email forwarding to send any emails to your main free account (I use Gmail) where you handle the actual email. Very few addresses I give out ever require a response sent using that address, and even if a response is needed you can just use the free Gmail address if you want to. This limits the exposure of your main Gmail address tremendously yet when you want to use a domain email address it is available. Also, if for some reason I get locked out of Gmail I can change the email forwarding very quickly to point to another free email service I use like maybe Outlook.com or another. There are specialized forwarding services like POBox.com (owned by Fastmail) that can handle all this too if your domain registrar doesn't include forwarding, plus you can send mail from your domain using POBox.com's SMTP server. There is also a method to send email from Gmail using Google's SMTP server, but if someone digs into the email headers they can determine what your actual Gmail address is. In any case, it is a way to send and receive domain email without paying a service provider like Fastmail.
https://support.google.com/domains/answer/9437157