Had the exact same problem after migrating my data to a new Macbook Pro, running Catalina ver. 10.15.3 and Outlook ver. 16.34.
Tried all the suggestions I could find (put Outlook Main profile from library and add it to PRIVACY tab in Spotlight and then putting it back), Terminal commands to rebuild index for Outlook messages (but certain parameters used are no longer working in latest MacOS), trying to use the recommended Outlook Repair utility (also not working since MacOS 10.14.
I found a link with detailed alternative solution proposals under
https://www.repairwin.com/fix-outlook-for-mac-search-not-working-no-results/
There the following solution under METHOD 6 / *TIP worked:
*TIP: Here is an alternative method to re-build the Outlook 2016 Database in MAC:
1. Go to the following location:
- ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile/Data
2. Move the Outlook.sqllite file to your desktop. (This will force Outlook to detect an issue and to do an auto rebuild).
3. When the Rebuild is completed, open Outlook and perform a search.
4. If the search is working then delete the 'Outlook.sqllite' file from your desktop
When I tried, first nothing happened (I had Outlook closed). I tried to open Outlook. A small dialog pops up telling me that there is something wrong with Outlook and it needs to be repaired. I clicked on the REPAIR button and Outlook started to rebuild the Main profile with its messages by creating a new Main Profile, copying the data and leaving the old profile under (BACKED UP) Profile.
Took a while. Afterwards the search works again.
Checking on the Outlook Main Profile under
~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles
I found a new Main Profile and the old backed up Profile.
Hope it might help....
