Android Error Building Signed APK: keystore.jks not found for signing config 'externalOverride'
I found the solution. I misplaced the path to the keystore.jks file. Searched for the file on my computer used that path and everything worked great.
File -> Invalidate Caches & Restart...
Build -> Build signed APK -> check the path in the dialog
Click on choose existing and again choose the location where your jks file is located.
I hope this trick works for you.