GMail app is way better the iOS mail. More features and iOS mail has not even heard of the snooze feature yet, a feature that every other email app has now. I have had dark mode on iOS gmail for months now...
To be fair Apple Mail simply cant do snooze. Snooze is done on the mail server and Apple Mail connects directly to your mail accounts; there is no Apple server involved.
Im sure there is some way they could support it through the app to talk back to the server, but my guess is it would be very complex and wont happen. It would be different for every mail service and be a mess.