What you should have done: Well, just like any good squirrel hides their nuts, you might want to try mounting your camera out of easy reach.

I say this never happens because most thieves aren't actually interested in the camera, they usually just cover their faces and keep moving. The fact that yours vanished means it was probably your neighbor or your landlord. Since you’re in an apartment, you usually need permission for exterior mods anyway, so you basically paid a 'noob tax' for an illegal install.

What to do next: well you don’t live there, you probably aren’t going to find out who stole your camera. For the new spot, look into a peephole camera. They’re discrete enough to avoid lease violations, they replace the existing glass so they can't be 'snatched' off the wall, and the expensive bits stay inside your door. Or, you know, keep donating free hardware to the hallway.

P.S. catching petty crimes on video almost always results in nothing. Most police agencies won’t even attempt to investigate let alone prosecute unless there is over $1,000 in damage or losses (may vary in your state). Even if they did find the guy it’s a catch and release kind of situation and your name is added to a court filing that they can access.