Yeah but the ADS-B transponder didn't know its own location because GPS was being jammed by the Russians to try to force the drones off course.

Why is the jet even flying in an active war zone?

This is the Russia war coming home to roost. They better admit that they are engaged in an actual war, and stop allowing civilian aircraft in areas that are attacked frequently.

Secondary surveillance radar does not depend on tracked aircraft knowing their own position, though.

ADS-B is an augmentation of that, which makes receivers simpler, but ATC generally does not rely on it exclusively (except in some very remote regions), nor on any type of active/cooperative signal or response – if everything else fails (maliciously or accidentally), there's usually primary radar as well.