No. Thankfully (at the moment) vendors are allowing us to install other OSes, but if a vendor really wanted to lock you down to Windows all they’d need to do is hide one option in the bios. I’m uncomfortable with the idea that there’s no technical reason preventing the PC industry from getting as locked down as Android phones did over time.

Only if the motherboard vendor allows you to. Imagine buying a Dell or Asus laptop and being forced to only run Windows.