That's fair! I didn't know they were offering that. I think it's a recent development -- it's not generally available ("contact us"), and it seems more focused at enterprise-type deployments than end-user mail that your typical Fastmail/Protonmail/etc.
But for the original question:
> Is there any email hosting out there with support for JMAP?
Stalwart really isn't a practical answer, at least yet.