Upgrading from Office 2011 for Mac to 365 from a mid-2012 MBPro to 2023 Air M2

This is my wife's computer, and she's been using Office for Mac for many, many years and likes it, has tens of thousands of emails and documents, and doesn't want to switch over to Apple Mail and Pages.

We're having a problem with the transfer because the new computer is not importing Outlook folders, only the individual emails. With 30,000 emails, this is a real problem. Even though we've created the .olm email folder on the old desktop (OS Mojave), by the time it goes through the external drive on its way to the M2, the folders have vanished (apparently a common problem with no solution we can find).

To complicate it further, we're trying to convert from the old POP account to a new IMAP account. Hours and hours (literally -- like 40, over a period of 3-4 weeks!) on the phone with a very patient Microsoft tech (Tier 3) and her email provider hasn't really helped. The MS tech says it won't help to update incrementally from 2011 to 2019 on the old computer, then to 365, and updating Mojave to Catalina, THEN importing the whole thing to the new computer with Sonoma and fully updated 365.

So we're still stuck. All we can think to do is import the individual emails in batches, then send them to new folders on the new computer. The tech said to contact Apple, but Apple says they don't advise on MS, and MS says they don't advise on Apple. Seems to me that this should be a Microsoft responsibility since they designed 365 to work on Macs and PCs, but we're having no luck.

Does anybody out there know any way to get this to work?