How do I stop Spotlight from showing browser search suggestions on Mac?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

dazzer wrote:

Thanks for the suggestion.

Unfortunately the error persists in Safe Mode, and also after rebooting normally.

I'm guessing the remaining option, sadly, is to reinstall macOS...?

Why would that be? macOS is mounted read-only from a cryptographically sealed snapshot. It cannot be modified. It will be no different after reinstalling. You might try Erase All Content and Settings, though I doubt that would help, either. Seems like it must be some configuration setting is not being set. There is a property list that stores the settings in your user Library/Preferences/ named com.apple.Spotlight.plist. Delete it then go into the Spotlight Settings and adjust the search categories.

I doubt this will work, but easy to try if deleting the plist doesn’t work. Delete the .Spotlight-v100 folder. You can show hidden items and find it at /System/Volumes/Data/ or use Terminal:

sudo mdutil -X /; mdutil -i on /; mdutil -E /

There are three commands there plus sudo to run the others as admin. The first erased the folder. The second turns indexing back on. The third erases the index and is only there to make sure indexing restarts.

Just copy the line and paste into Terminal. When it asks for a password, just type the password and hit return. You won’t see anything as you type.

If you erase the folder, you may have to log out and back in to restart indexing.

You are almost there

System Setting >> Spotlight >> Websites and untick

Uncheck Siri Suggestions in addition to Websites. You might even deselect Help Apple Improve Search, though uncertain if it is an issue or not with web results showing up in Spotlight searches after the preceding sentence.

Is it finding the desired items and also showing web search result?

I have Websites and Siri Suggestions disabled and I will see a Search Web option when I don’t get a match, but not search results.

I’m wondering if the index is corrupted. Have you tried reindexing?

dazzer wrote:

Thank you.

I posited whether a clean install -- Erase all... -- would do the trick. Maybe not.

Unfortunately deleting plist didn't work, nor the Terminal trick you suggested.

No idea, then. I don’t really see any excessive web results on mine. hey only appear if it doesn’t find anything on my Mac.

Welcome

Sorry, out of ideas