There are advantages to having your own domain - you can use something like vendor8832@yourdomain.com so each site you sign up to gets their own unique “to” address, that way you can easily send their mail to trash when you dont’ need to deal with them anymore, and will also let you know what company had a data breach if that unique email address starts to get spam.

Not worth the hassle - best compromise is to get your own domain but use a provider like fastmail to host it.

If they turn sour you can move your domain to another mail host.