'XR' does not exist in the namespace 'Unity' - toolkit issue when upgrading from unity 2019 to 2021

ive recently upgraded my unity version from 2019.4.2f1 to 2021.3.3f1
I followed this tutorial on how to upgrade unity version: tutorial
after that I was presented with errors regarding something not existing in Unity.VR
One of it was: Error (1)

Assets\3D\XRHandPoser\Core\Audio\Scripts\GrabAudioEffect.cs(7,22): error CS0234: The type or namespace name 'Interaction' does not exist in the namespace 'UnityEngine.XR' (are you missing an assembly reference?)

Then, i proceeded with the following steps:

• install XR Plugin Management package

• install XR Interaction Toolkit package via name (upgraded to 2.1.0-pre.1)

• Error (2) :
  
  

  Warning: XRRig has been deprecated, use the XROrigin component instead.

• follow this suggestion : suggestion (Add using Unity.XR.CoreUtils; to the script)

• Regenerate project files (under External Tools settings)

• Note: I regenerate all

• Error (3) :

Script updater for Library\Bee\artifacts\1900b0aE.dag\MikeNspiredXRHandPoser.Runtime.dll failed to produce updates.txt file

and

Assets\3D\XRHandPoser\ExampleScene\Scripts\PlayerRigMovement.cs(3,13): error CS0234: The type or namespace name 'XR' does not exist in the namespace 'Unity' (are you missing an assembly reference?)

I deleted the Library folder as a suggestion i got from multiple places, restart the unity, and got this message

• I click on 'Go Ahead' and it took like so many hours (around 4 hours before i click on the project settings@ menu and it went away, but it came back once in a while)

• I dont know how to proceed, so i deleted the Library folder again, restart, and i got the message again.

• i chose 'No Thanks' this time and was left with Error(3)

• P/S: i also follow this suggestion (removing spaces from installation folder and removing the read only to the folder but the errors persist.