try afterburner
maybe the AMD control center itself
Also, make sure GPU-Z is fully up to date, to include even removing and re-installing the most recent version with the current GPU installed (you mentioned a change earlier, could be a sensor issue as the tool is currently installed).
What is the other GPU?
RX6600 isn't exactly a high end model, if they decided to skimp on a sensor readout, that would not be surprising. Basically would be the memory and fan power in addition to the GPU.