Using New Outlook on Windows for professional communication and productivity
While I do notice the "Personalized email address" settings within Outlook, I don't see any related configuration beyond what's available for GoDaddy, which I don't use:
I have instructions to use another name server but if you have a grandfathered custom domain, you don't want to do that. You'll need to keep the subscription active to keep the custom domain if you switch to the option in Outlook settings.
I have some of the old custom domains - I'll test it with them.