I've tried the fixes here and so far nothing has worked. My problem may be compounded by the fact that the files I want are all on external hard drives, not on the internal. Someone elsewhere suggested a solution to the question to add the Macintosh HD file to the Spotlight Exceptions in System Preferences, wait 30 seconds, and then remove it. I've done this and, as they promised, Spotlight now says that it is indexing my drive. But trying to do the same thing for the external drive is getting me nothing.
One issue I have is odd in that I was briefly using Microsoft OneDrive as a redundant backup for the external drive (I know—MS, what was I thinking?). That caused another whole slew of problems so I quit using that but the "OneDrive" folder still exists on the external drive because OneDrive or MacOS wouldn't allow some of the files to copy from that drive to a new drive (again, I blame MS! ugh...). What's odd is that sometimes—not every time—the Finder will find the old file I that I want in THAT drive but not its duplicate in my working drive folder.
Anyway, I don't store working client files on my Macintosh HD so while I'm glad it's indexing, I need Finder or Spotlight to search the external hard drives and find files when I can't. I know it's NOT working because I literally created a folder a few minutes ago and my search for that folder in the folder it resides turned up empty.
Never had this problem before and I'm shocked that such a basic feature has gotten so fouled up.