Calendar search doesn't work at all

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

ddd3 wrote:

Calendar search doesn't work at all. I have tried reindexing Spotlight using OnyX; no help.

how do I know if I have reached the maximum entries allowed?

Which Calendar... the built in macOS Calendar.app

or

third party...?