This question already has an answer here:
Is there a way to disable a laptop's (MBP) built-in screen when using an external screen without closing the lid? I would like to keep using the trackpad due to accessibility reasons.
Alternatively is there a way to make the external screen the default one and prevent windows and other things from popping up on the laptop screen? if yes, then I could simply ignore the built-in screen without disabling it.