Mail not syncing

Hi,

I've got a iPhone XS Max with latest iOS, and a 2013 MacBook Pro with latest MacOs. I have a issue with mail (iCloud) not syncing. Seems anything I do on the Mail app on my phone doesn't seem to sync with Mail on MacOs.

So for example, if I read or delete a message on iOS, the MacOs Mail will still show them as unread and in the Inbox.

If I read and delete a message in Mail macOs Mail in iOS syncs that data fine.

I can't seem to work out what's wrong.