In the FreeBSD section he mentions loading the AMD GPU drivers lower the power. I have less experience with AMD GPUs, but with Nvidia cards on FreeBSD I’ve had to load drivers, then open the GPU device (/dev/nvidia0) to get powermizer to kick in. This takes an old Ampere card from running at full power during idle (p state 0), to entering its lowest power mode (p state 8). among other things, this drops the temperature on the card by 15-20° C. Nothing has to be done with the device, just having an open file handle to it is enough.

On Linux this doesn’t seem to be an issue. Additional Nvidia utilities do this already.