Android Studio missing essential plugin org.jetbrains.android

Just delete this file (or delete last disabled plugin(s) in this file):

C:\Users\YourUserName\.AndroidStudioVersion\config\disabled_plugins.txt

Update 10 Feb 2021:

If you couldn't find this address try this on windows:

C:\Users\YourUserName\AppData\Roaming\Google\AndroidStudioVersion\disabled_plugins.txt

Recently this Address transferred to here.

Update 04 August 2021:

If you are using windows 11 App data folder is hidden and needs to be prompted(just search how to take out missing app data folder in windows 11) Then go to the same location as earlier mentioned and delete that file

For Windows users.

C:\Users\YourUserName\AppData\Roaming\Google\AndroidStudioPreview4.1\disabled_plugins.txt

Deleting this file will fix the issue.

More detailed information.