I have been struggling to get autoarchiving to work. Here is my setup:
Email is office365 exchange via Godaddy
Running Outlook (Office) 2019 on a new Windows 10 desktop

Some messages in my Inbox just won't autoarchive.
I have imported messages from a backup .pst file when I set up this new exchange account. It was previously a POP account.
I set Autoarchive to run every day and for messages older than 2 months
I selected a file called Archive.pst

I recalled a problem like this a few years ago where autoarchive went by Last Modified date rather than received date. So I looked that up and added this to my registery
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\O utlook\Preferences

Value name: ArchiveIgnoreLastModifiedTime
Value type: REG_DWORD
Value: 1

Imported messages older than 2 months still won't autoarchive