Hey again! I’d recommend updating for sure as said if not already!
If the problem continues, I suppose knowing if the issue happens in a new user account and/or in safe mode occurs, although I know it started directly after updating the OS, I may try this personally:
First, I always keep a current backup of my data.
Quit all apps, open Finder.
While holding the Option Key, on the top menu click Go > Library.
Next, open Metadata > CoreSpotlight and delete the index.spotlightV3 folder.
Restart, I’d give it a day or so before testing.
Otherwise, if the issue continues, I’d boot to recovery mode:
For your Mac, shut it down. Press the power button and continue holding until you see Startup Options.
Click Options, enter your Mac password.
From recovery, first make sure your volumes are mounted:
Open Disk Utility, click what’s typically Macintosh HD and Macintosh HD - Data, next click File > Mount, and enter your Mac password again, (You only need to do this if they volumes are greyed out, meaning FileVault is on).
Next, hit Disk Utility on the top menu > Quit Disk Utility.
Then on the top menu, hit Utilities > Terminal.
Once Terminal opens, type this command and press Return afterwards:
rm -rf /Volumes/*/.Spotlight*
Once done, you’ll see the standard bash#, but it should be quick, then restart.
Next, open Spotlight search (Command and the space bar) and type something to confirm it started indexing. It should, but then you should give it a full day to finish the job.
If you need to copy and paste the command, while in recovery, you can open Safari and log into your mail account.
Hope one of those do the job!
