I think I know why the fans are going crazy. It's my old nemesis returned from the grave: tracker-extract! This time it's tracker-extract-3 instead of tracker-store. It seems that nautilus depends on it. Oh nooooo! I checked all the dconf editor stuff I noted last time and they're still set. So… I guess they moved stuff around? I hate it.
https://alexschroeder.ch/view/2018-05-07_Laptop_Fan

The amount of stuff to read in order to understand how to disable this is amazing.
https://unix.stackexchange.com/questions/694065/how-to-really-completely-disable-gnome-tracker