Search Feature on Outlook for Mac does not find all items

I am using Microsoft Outlook for Mac Version 16.38 on my work computer, which is iMac (21.5 inch, late 2013) running macOS Mojave 10.14.6.

The search often only returns a subset of the entries that is should return (which are returned correctly when I used the web based version of Outlook). I tried the fix of dropping the "Main Profile" folder into Privacy in Spotlight and then deleting it. This did not fix the problem.

I contacted Microsoft and they suggested dropping the Macintosh HD icon into the Privacy tab and then deleting it.

But I am afraid to do this because of the message I get when I go to drop it in:

Are you sure you want to prevent Spotlight from searching in "Macintosh HD"?

If you exclude this location from Spotlight searches,

the search feature won't work in some applications.

Is okay to do this ? Or is there a safer way to fix the problem?

Thank you.