I've run into a problem that, after some research, I discovered has been encountered before with Mojave. Ever since my upgrade to Catalina a few days ago, search in Outlook 2016 has quit working. I've been online and have tried everything I found - forcing Spotlight to re-index that folder, completely rebuilding the Spotlight index, deleting Outlooks SQLite db and letting it rebuild. I even removed Outlook (including all data) and re-installed. None of it has it worked. I did notice, however, that Spotlight searches themselves worked just fine.
Is this a known regression? If so, does anyone know if it's being worked on? If not, where do I need to report the bug? (or if anyone knows a workaround, I'm all ears (eyes?).)
I worked with MS support and found a solution that fixed it. I had uninstalled Outlook and deleted all its data, but that didn't fix it. They recommended removing the entire Office suite and deleting the data, then re-installing the whole thing. That solved the problem.
So... in case somebody else runs into this problem, this is at least one way of fixing it.