Not with MX but, look at google's split domain documentation. You can either have them handle the domain and forward you a copy, or you can have your own domain

Not with MX but, look at google's split domain documentation. You can either have them handle the domain and forward you a copy, or you can have your own domain be the primary and forward to google. I have been using the latter for a few years now since not all of the users in the domain are using Google Workspace. They have a special address for forwarding to so you don't get into a loop. It has been working flawlessly for us.