There is a fix coming for the 5500m heat/wattage issues in the next OS thankfully. The MacOS drivers for RDNA are apparently just crap. This problem wasn’t present on the Vega GPUs, and it isn’t present while booted into Windows. To think this lasted all the way through Catalina and Big Sur is insane.
I would also like to know that. AFAIK the 5500 has the same driver issue as the 5300, but even without a fix its baseline consumption with an external screen plugged in is about half of the 5530's.
Hopefully the fix applies to both models but I'm not holding my breath.