I've known people who left for a brief period during the GC process on emergency basis and then were put into a literal jail on their return to the USA.
You'd be lucky today if that literal jail was IN the USA.
The process is very straightforward - without advanced parole or a valid visa you can’t come back in.
Or if you’ve violated immigration or criminal law you run the risk of being detained.
But that’s how the system is supposed to work.