heat of Mac m1 after macOS 27

Heavy processing loads generate heat, that’s normal. You can see what is using significant processor resources by opening Activity Monitor, and sorting the CPU tab by % CPU. Known compute-intensive tasks like gaming, video transcoding, etc., will cause your Mac’s processors to heat up. Your Mac will manage its thermal state. On MacBook Pro models, the fan(s) will spin up to cool the Mac. MacBook Air models with Apple Silicon lack fans, but if needed macOS will throttle back the processors to cool them down. 

You should always ensure that the ventilation openings are not blocked (even for the MacBook Air, since that relies on convection cooling). Use your Mac on a hard surface, not on a pillow or blanket. The bottom of the case may get warm, there’s a reason Apple calls these ‘notebook computers’ and not laptops. 

Some programs are inappropriately processor-intensive, for example Google Chrome is a known resource hog on Macs (in part because it installs several extensions that run in the background to support Google’s information-selling revenue model, and those run even if you don’t launch Chrome; see https://chromeisbad.com). Similarly, ‘helpers’ like the misnamed CleanMyMac (aka BrickMyMac) and antivirus software are not only not needed but can be detrimental to your Mac.