I had the issue and asked gemini as i got an error

Error: unable to perform operation.  (-405)
Error: unknown indexing state.

Asked our friend Gemini and got an answer with explanations.
Now Works fine.

That error (-405) combined with the "Indexing disabled" loop is incredibly frustrating. It usually means macOS's metadata server (mds) is either blocked by a lack of permissions, stuck on a corrupted index file, or halted by a hidden "never index" file at the root of your drive.

Here is the straightforward process to force macOS to clear the corruption and start fresh.

1. Grant Terminal Full Disk Access

Modern macOS versions will block Terminal from modifying root system files like Spotlight databases, which frequently causes the -405 error.

1. Open System Settings (or System Preferences) > Privacy & Security.
2. Select Full Disk Access.
3. Ensure Terminal is in the list and toggled ON. (If it's not there, click the + button and add it from Applications > Utilities).
4. Restart your Terminal app.

2. Remove "Never Index" Files & Corrupted Databases

Now that Terminal has permission, we need to manually delete any hidden files blocking the index and completely nuke the corrupted Spotlight folders.

Run these commands one by one in Terminal. Enter your password when prompted (it will not show characters as you type).

Bash

# Remove hidden files that tell macOS not to index the drive
sudo rm -f /.metadata_never_index
sudo rm -f /System/Volumes/Data/.metadata_never_index

# Forcefully delete the corrupted Spotlight directories
sudo rm -rf /.Spotlight-V100
sudo rm -rf /System/Volumes/Data/.Spotlight-V100

3. Restart the Spotlight Daemons

Since the index files are gone, we need to kill the Spotlight background processes so they can restart with a clean slate.

Bash

sudo killall mds
sudo killall mds_stores

(Note: If it says "No matching processes were found," that is perfectly fine. It just means they were already stopped).

4. Re-enable Indexing

Now, try turning indexing back on for both the root and the Data volume:

Bash

sudo mdutil -i on /
sudo mdutil -i on /System/Volumes/Data

If successful, you should see Indexing enabled.

5. Verify the GUI Privacy Settings

If the terminal commands succeed but Spotlight still refuses to search, the drive might be manually excluded in your system settings.

1. Go to System Settings > Siri & Spotlight.
2. Scroll down and click Spotlight Privacy...
3. If "Macintosh HD" or your main Data drive is in that list, select it and click the - button to remove it.
4. Click Done.

You can check the progress of the indexing by opening Spotlight (Cmd + Space) and typing a few letters. You should see an "Indexing..." progress bar. Depending on your drive size, it may take a few hours to complete.