What is this thing?

Just trace it out. It is likely some old alarm. You're probably going to find a black box zip tied under the dash somewhere. There will likely be a relay zip tied near this somewhere.

All aftermarket alarms are installed like this. It makes the car super easy to steal. The little relay is the ignition circuit for the car. The two larger wires on the relay is the main ignition wire the key switch activates. It would be much more difficult to find that wire without the black box and relay. When you get into the floorboard and really look under there, the aftermarket junk will be dead obvious.

The systems used to track a vehicle are nothing like this. There would not be a switch either. I have installed these tracking systems before as a side gig when some of my dealers didn't have much paint work for my auto body shop. The tracking alarm needs to be mounted just under the dash where the GPS and GSM antennas have as little metal between them and the sky as possible. The easiest way to do this on most cars is to remove the gauge panel. Smart dealers don't install the system in any obvious way or even use them to disable the vehicle. They just keep a spare key filed and repo the car if you don't pay, don't answer the phone, fail to call head, or act like an asshole about not paying.

Yes, it absolutely could have a tracking device in it. This could also be part of an alarm system or ignition interlock..but if you’ve been driving it without hitting the button, that doesn’t make sense. I would have a mechanic run the wires to see where they lead and remove it. It’s not factory

Might be part of an immobilizer system. A lot of “buy now, pay later, we don’t reject anyone for bad credit” places use them. Not that Carvana is like that (I bought my car from them and had a great experience, though I’ve heard other scammy things since then) but since you mention a “third-party” maybe there’s something funky going on.

Just looks like a switch to me. I don’t know what it’s switching but could follow the wires and see where it leads. If not comfortable with car electronics, just take it to a mechanic and they should be able to reverse engineer it and remove it if unnecessary.

Like another poster said it’s definitely not factory. You can tell just by how janky it looks and how it’s screwed into the fabric and plastic molding.

Could be for some accessory that was removed prior to selling to Hertz and they forgot about it. But could also be for some tracker.

It sounds like an emergency way to open the truck if someone gets stuck/locked inside.