“No expectation of privacy in public” is a legal doctrine. I do have an expectation of privacy in public. Stop filming me and shit, mind your own damn business.

Between computer and device running Android.

Adb is just an interface between computer and phone, the packages it lists may not be every system component, you can add anything in at kernel level, or also just not list it in that interface.

Not if they’re baked into the system. Although that may get into GPL violations, I forget. God knows a device can come with locked firmware though.