Outlook 2016 Search no results 16.16.8
There is a problem with Outlook and Mojave talking to Spotlight (maybe specifically after an upgrade?), I've also found that this is an issue with Fusion Drives as well as it slows down Spotlight indexing. Microsoft is aware of the issue and is looking to investigate.

https://support.office.com/en-us/article/search-doesn-t-work-in-outlook-for-mac-after-macos-upgrade-b73de6f1-aeb9-4720-bbbe-de65ab50012e

I've tried all of their steps in your link previously, currently, I'm using Onyx to fun the full maintenance scripts (Launch Services, and Spotlight Index). It's worked for me, for now...