Fix Android Studio error: Missing essential plugin: org.jetbrains.android

Just update Android Studio 4.2.1, but fail to run with error of: 

Missing essential plugin: 

org.jetbrains.android 

Please reinstall Android Studio from scratch. 

Here how I fix it in my case, Android Studio 4.2.1 on Windows 10:

Search and delete "C:\Users\user\AppData\Roaming\Google\AndroidStudio4.X\disabled_plugins.txt"

There are two in my setup:

"C:\Users\user\AppData\Roaming\Google\AndroidStudio4.1\disabled_plugins.txt"

"C:\Users\user\AppData\Roaming\Google\AndroidStudio4.2\disabled_plugins.txt"

I delete both disabled_plugins.txt and re-start Android Studio.