Outlook Desktop - Searching Large, Shared Mailboxes Either Not or Poorly Functional

Not a new topic, but looking for any new insights!

We have a significant number of large, shared mailboxes in EXO - and Outlook desktop users who need to do frequent searches of these mailboxes. With Outlook desktop's caching behavior [regardless of whether or not 'download shared folders' is checked/unchecked], search functionality is either not working at all, or not providing complete/accurate results if it [sort of] works.

Of course, Outlook desktop users mutiny over trying to use the Outlook Web App for shared mailbox functions.

Does anyone have a solid solution or recommendation for the searching of large, shared mailboxes?