Smart Mailbox not working with Gmail on Apple Mail - resets to no mailbox selected

I'm trying to sync Gmail with the Apple Mail client and setup a Smart Mailbox of important emails that are unread. The Gmail emails sync correctly, in various folders as on Gmail. However, when I try to create a smart mailbox, they don't filter in and when you go to edit that smart mailbox, the filters reset. See images below: Resets to 'No mailbox selected' The Gmail mails are syncing and filtering correctly, as on Gmail. The smart mailbox works for iCloud accounts though and Apple support wasn't helpful. They said it's Google's problem (even though that doesn't make sense) and even refused to create a ticket for further investigation. Google says that since the emails are syncing and filtering, the problem isn't at their end, it is with the way the Apple Mail client works (and that makes sense). Can anyone please help me with a fix here? [Device: MacBook Pro M2 Pro 2023, MacOS Sonoma 14.0]