Try opening Whisky and:
File > Kill All Bottles
or press Shift + Command + K

That stops the CPU usage (presumably closes the other end of the pipe) but of course also closes all running apps.

That stops the CPU usage (presumably closes the other end of the pipe) but of course also closes all running apps.

Whisky reads from stdout and stderr of the child Wine processes for writing to logs. It's probable that's what's causing the excess CPU usage you're seeing here. I doubt it's actually using CPU and probably just doing the equivalent of spin waiting on a thread.

NSPipe is always kind of jank and seems to break whenever I touch it so I try to avoid messing with logging it I can.

According to the energy usage meter it is using actual cpu cycles. More precisely it seems we loop in. AvailableData should block but I supposed it doesn't block on pipes because they are open? Because the profile just shows we are doing a bunch of fstat and readsyscalls. The other option of course is if wine is just pumping a bunch of data (which wouldn't surprise me)
x.ref https://developer.apple.com/forums/thread/690310 for a different implementation of this from an apple dev (this I just found while looking through stuff)

Can confirm this 100% load is real, judging solely by the laptop temperature. Whenever I open Steam through Whisky and leave the latter in the background, my mba gets hotter. I see the load in the activity monitor, too.

The workaround there is to close Whisky after Steam has loaded. Whisky doesn't kill Wine processes when quitted, so everything works flawlessly.

I have latest Sonoma and Whisky versions.