MacBook Pro mid 2012 keyboard issue I'm using MacBook Pro 2012 model with macOS Catalina. A few keys (I don't know which ones exactly) key on my built-in keyboard seems to be pressed continuously. I have disabled the internal keyboard using kextunload in Terminal and currently using an external USB Windows keyboard. 

Here's the issue:
Every time I restart my system, the built-in keyboard gets enabled automatically (So I have to use kextunload again and again). Also, during startup, I'm unable to start in safe mode or Recovery mode or change startup disk using an external keyboard (I guess this happens as a result of built-in keyboard getting enabled at startup and hence the pressing of some keys on it).

Is there a way to permanently disable the built-in keyboard and make the external keyboard as an only input source?
It has nothing to do with your build in keyboard. What u have encounter is due to MacOs Catalina. I have same problem. It started from bottom row of alphabetic of your keyboard. You get multiple Z after pressing the Z button once until you have to press the return key to stop it. It sorts of like a virus escalated to the rest of your buttons on the keyboard. Slowly all your small caps alphabetic auto Caps Lock although you have not activated the Caps Lock and numerics auto change to symbols without pressing shift button. The WORST OF ALL COMMAND button + R button (have been remove from your drive) after the update to MacOs Catalina that does not allow u to access to internet recovery utilities. Further Damage done by Catalina is that many apps not be able to support. So congrates! All u could do is to restart your macbook pro whenever should these problem arise each time.