Spotlight doesn't show applications Setup

I've got a MacBook Air (13-inch, 2017)

Problem

When I type in the name of an application, Spotlight doesn't show the application. When I do sudo mdutil -E /, It says the following, 


  Error: unknown indexing state.


When I Select System Preferences, Click the Spotlight pane, select the Privacy tab and then click the Add (+) button and try to select anything, It says


  Privacy List Error,
   the item couldn’t be added or removed because of an unknown error.


What I tried

I've tried https://www.macrumors.com/how-to/rebuild-spotlight-search-index-on-mac/,
and Spotlight re-indexing takes too long or doesn&#39;t work. sudo rm -R .Spotlight-V100/ says 


  No such file or directory


sudo /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -seed -lint -r -f -v -dump -domain local -domain system -domain user -domain network


does a lot of stuff,

sudo rm -R .Spotlight-V100/ also says


  Error: unknown indexing state.


sudo mdutil -E -i on / 
says


  Error: unable to perform operation.  (-400)   Error: unknown indexing
  state.


How it happened

When I tried to download the macOS Catalina update, the mac got stuck in an endless loop of trying to update and then failing, forcing it into recovery mode, I tried to stop the update by using this link, https://www.mklibrary.com/technology/macos-sierra-stuck-endless-rebooting-loop/ but nothing worked, so I had to fully reinstall macOS, Spotlight now doesn't show any files or applications at all. It only shows other stuff like emails, Dictionary suggestions, etc.

(Note, I've also made sure to check all the categories in system preferences)

I've tried,

sudo mdutil -a -i off,

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist'''

sudo mdutil -a -i on

It worked, however, it stopped working again afterwards when my computer shut down.
I am not sure whether you have tried this step or not. 

Open Terminal window from LaunchPad. 

First, turn off Spotlight:

sudo mdutil -a -i off 


Next, unload the metadata file that controls Spotlight’s index:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist 


Use the following command to re-loads the index :

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist'''


As a last step, turn Spotlight back on:

sudo mdutil -a -i on 


After a few minutes to rebuild the index, Spotlight should be functioning as normal.

Let me know how it goes. 

Update: I have a script for it and it is helping me in such kinds of issue. 

#!/bin/bash
# This script is designed to fix Spotlight indexing issues
# by removing the existing Spotlight index and forcing Spotlight
# to create a new search index.

# Turn Spotlight indexing off

/usr/bin/mdutil -i off /

# Delete the Spotlight folder on the root level of the boot volume

/bin/rm -rf /.Spotlight*

# Turn Spotlight indexing on

/usr/bin/mdutil -i on /

# Force Spotlight re-indexing on the boot volume

/usr/bin/mdutil -E /


Save this as .sh and run from the terminal. It should help you to fix your issue too.