AutoArchive working but not for Delete Files folder

I'm trying to create GPO for Outlook to enable AutoArchive for all our users to delete Outlook messages older than x months. I've created the GPO and allocated it. Outlook for the affected users appears to show the correct AutoArchive settings for each folder. The AutoArchive prompt appears and runs when expected. The majority of folder's messages older the x months disappear with the exception of the 'Deleted Items' folder. No messages removed from there. Why is this?

I have no control over the server so can't set up deletion from that end. I've been told nothing on the server is stopping the Deleted Items from being removed.

Windows 11 Education 24H2, Outlook from Office LTSC Pro Plus 2024.

Any suggestions welcomed.

Thanks.