Terminal – MacBook Pro mid 2012 keyboard problem


I'm using the MacBook Pro 2012 model with macOS Catalina. Some keys (I don't know which) on my built-in keyboard seem to be pressed continuously. I deactivated the internal keyboard using kextunload in the terminal and I am currently using an external USB Windows keyboard.

Here's the problem:
Every time I restart my system, the built-in keyboard is activated automatically (so I have to use kextunload again and again). Also, I can't boot into Safe Mode or Recovery Mode during startup, or change the startup disk using an external keyboard (I guess this is because the built-in keyboard is activated at startup and therefore some keys are pressed there).

Is there a way to permanently disable the built-in keyboard and set the external keyboard as the only input source?