How do i set up custom email domain as a separate account in native Mail App

How can I set up custom email domain as a separate Mail account.

Hi

I recently set up a custom email domain with Cloudflare and iCloud to use but the email address is effectively an alias for my iCloud email address and this isn’t what I had in mind.

Is there a way to set up a custom email domain to act as its own individual account in the native mail app like an ISP email address gets set up like shown in the pictures.

Please don’t suggest using ‘rules’ as there is too many flaws with that lazy workaround for me.

I was thinking along the lines of using something like Proton Mail for hosting my domain but their bridge doesn’t support the iPhone Mail app and I use the mail app on my iPhone and MacBook so need a solution that works on both devices seamlessly in the same way my ISP email address works. Other Hosting sites I’ve looked at are never clear in these areas so I’m hoping someone has done it and knows how.

Is what I’m trying to do possible or did I just waste my money paying for my domain?