I recently bought a new System76 laptop as a stopgap, but it might end up becoming permanent. Kind of a sad end for 25+ years of Mac use.
I’m torn. I don’t want to return the machine because everything else is crap. At least the 16” works well as a laptop so long as you don’t plug anything into the ports. But Apple’s Q&A has seriously gone down the toilet ever since Steve Jobs died. Clearly him throwing staplers at people was the glue holding Apple together.
Unfortunately, while the kernel panics will most likely be fixed eventually (10.15.4 is a complete shitshow, even by Catalina standards), it seems the dGPU is actually working as designed with the high idle power draw. If you search for “navi multiple monitor power draw” you can find reports of desktop AMD cards that predate the 16” MacBook Pro that exhibit the exact same behaviour. It’s something to do with memory clocks and mismatched resolutions/refresh rates between monitors, and I very much doubt it will ever be addressed via software (if it even can be).
Very annoying as it causes the fans to spin up audibly when you put it under the slightest stress.
Like you I don’t know what to do. I’m able to return it due to the extended return window they have currently, but I have absolutely no intent of switching to Windows or Linux.
At least when operating in clamshell mode with one external monitor, I can get the power usage to drop from 20W down to 5W by using switchresx and dropping the refresh rate from 59.88 to 56.88 Hz. When I do that, even light WebGL work doesn’t cause it to exceed 7-8 watts.
It sounds like some work around for the special case of a single external monitor with the internal display closed isn’t kicking in like it’s supposed to.
My understanding of the issue is that the card has variable memory clocks to save power. However, to avoid visual distortion/tearing, the clocks can only be changed during the monitor's v-blank. However, when you have multiple monitors, presumably you would need extra circuitry or at least some mechanism ensure each monitor is in sync, or to detect when the blanking intervals match when using monitors with different refresh rates. I don't have a strong knowledge of this sort of thing, so I don't know how exactly this is achieved, but in this case AMD has "solved" the problem by simply running the memory clocks at full tilt 100% of the time, thereby avoiding the need to precisely time changes in speed.