The current Setapp version of iStat menus reports 144 degrees, which is at least as hot as my old 2013 iMac was running. Does this indicate a problem?
It’s in clamshell mode, but suspended on felt-covered rails so only one inch of the sides is touching, leaving it almost completely surrounded by air under my desk.
What’s it doing at that temperature?
Safari browsing, OmniFocus. While culling photos in Adobe Lightroom (scrolling the thumbnail grid, selecting, zooming in and out) it got to 156 a couple of minutes ago. Now down to 148 as I type this response.
But no video or audio encoding. However, I am using a Luna Display to send the screen to my 2013 27" iMac. But the GPU’s cool. It’s the CPU that seems hot. See attached screenshot
Have you updated your Lightroom to the Apple Silicon native version?
P.S. I dislike clamshell mode but understand why you might want to use it.
Activity Monitor showed loginwindow was using 93.5% CPU, with CPU time of 79:05:11:61, and Luna Display 23.4%.
Restarted an hour ago and now I’m down to 89 degrees. But why would loginwindow go crazy?
My Lightroom is 11.0.1 (the latest, I think), but don’t know if it’s native Silicon. Creative Cloud only offered the version I have, and saw no mention of a separate AS native version. Is it “universal”?
Universal means native on an M1 Mac. That’s good. Click on the app in the Applications folder and press CMD+I to display the information panel. You’ll see Intel, Apple Silicon, or Universal next to the app name at the top.
On my desk I have my M1 MacBook Air sitting on an old Belkin ventilated base with two fans built into it that runs off USB power (plugged into the wall). I only plug it in very occasionally. And these days, I think the MacBook Air is “getting warm” when iStat Menus reports that it is heading past the 80 degrees Fahrenheit mark. My old 2018 MacBook Pro would routinely hit 150, 160, and into the 170s, pushed there by Adobe software. And that machine had built-in fans!
I’m probably being overprotective. 
Shutting down the loginwindow process that had run amok did the trick. After 6+ hours of routine work, it’s running 87 degrees.
Thanks to all!
This is yet another long-standing bug, sometimes loginwindow fails to go away when it should.