You can do something to make macOS less hot and the battery more durable. (Pun unintended.)

sudo fs_usage -w -f filesys <Process Here>
  1. mds_store: ignore those directories (mostly caches). On my MacBook, mds_store normally takes only 0.1% of CPU now.
  2. kernelmanagerd: uninstall those kexts. The offender here was Karabiner Elements.

For WindowServer, use log:

sudo log stream --predicate '(process == "WindowServer")' --debug # or --info

Update on WindowServer

WindowServer also handles user input. There's clearly a CPU usage spike when you move your finger over the touchpad. But I saw quite a lot of "surface is not detached, CoreDisplay is detached". This seems to be a problem with external monitors. Well, but I don't have an external monitor connected at this time! So I don't know what to do now. I will update this post again when I have access and see what I can do then.

Quick-tip: thanks to Ишуай Ли's comment (see below), charging from the right side will reduce CPU usage by kernel_task.