Spotlight not listing documents on MacBook Air after upgrade

Did 'Documents' become unchecked when the Tahoe upgrade was applied?

Sometimes settings might get tripped during an update.

Apple provides additional guidance for Spotlight issues:

If searching your Mac returns unexpected results - Apple Support

Also, see if the problem still happens in safe mode.  Safe mode will often correct weird software behavior by forcing the OS to clear caches, do disk repair and other self-maintenance and housekeeping and temporarily disables third-party mods.

How to use safe mode on your Mac - Apple Support 

You can exit safe mode by restarting your Mac normally, then reevaluate the problem.

Scroll down to the bottom of the right panel and find the Search Privacy... button.

Click that and see if any of your folders have been listed there.

If so, they are being excluded from Spotlight's search results.

Prevent Spotlight searches in specific folders or disks on Mac - Apple Support

Try rebuilding the Spotlight index.

This is Apple's guidance: Rebuild the Spotlight index on your Mac - Apple Support

Do you see the button with a folder icon when you click the Spotlight icon?:

On my Macbook Pro running 26.3, I can click that and files appear. Entering a file name narrows the search like before. No, I don't like the interface but it works well enough.

Spotlight changes have been a contentious part of the Tahoe rollout. To let Apple know the scale of the concern over such change, please take advantage of this feedback link that reaches an Apple Employee:

https://www.apple.com/feedback/macos/

They won't see you issue in this user-to-user setting among tens of thousands of new posts daily.

Hmmm... 🤔

Are you running any anti-virus, cleaning, optimizing, security or VPN software?

It's possible that there is some interference being caused by an app of this type. These types of apps aren't needed on the Mac. they do nothing the macOS cannot do and often cause problems.

Also, I'll refer you to another community thread. There are some suggestions and info there that you may find helpful. Spotlight not finding documents on Mac despite indexing - Apple Community