It is a free market issue, because when an oligopsony controls what can be bought and sold you don’t have a free market. These hardware vendors are controlling the market for software for their devices, and buyers are not free to make their own decisions about hardware they purportedly own.

You are also free to alter the device in any way you want as long as it doesn’t start emitting radio waves.

Modifying the hardware != running the software I want on the hardware I own.

So yes, your last statement is correct, but utterly irrelevant to this discussion.