Spotlight not finding folders, files, or apps in High Sierra
I found the answer on this post in an Apple Community forum.

The key was to rebuild the Launch Services Database - I didn’t even know that was a thing. You need to use the terminal and run this command:

sudo /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain u -domain s -domain l -v


Takes a minute or so to complete and you get a lot of lines with errors. Then I continued with the advice in the post to rebuild the indexing with the following

sudo mdutil -i on /
sudo mdutil -E /


After running for just a few minutes I started to see apps show back up in Spotlight.

Hope I can save someone else a few weeks of pain and searching.