Sorry for the late reply. Did you get the phone to supply power via its USB port with postmarketOS? I did not get that to work. According to the wiki, this is a known issue: “The phone won’t supply its own power, so you need either a powered hub or an extension cable wired up to 5v. Some hubs may refuse to work without power being supplied from the port however.” See the OTG doesn’t work on the Wiki page

Are you using external power with the Adapter? I ran into this issue with my oneplus 6t, which cant supply power to a usb device. Using a external chsrger with a Combo dongle works fine right now. You may need to enable host mode though

I doubt any modern car with those features have a physical sim card you can remove. They are probably all using some sort of esim. On some cars the antennas can be unplugged but that depends on the specific model. If you’re unlucky, you will not even be able to remove the tracking features at all because they are integrated with other components needed to function.

With regards to the legality of that, I unfortunately cant help you there. Probably best to search for local cases or ask a local lawyer.

Your best option in probably buing a used car thats old enogh not to track you. Hope that helps a bit