I've kept an eye on it and it doesn't seem to be anything in particular - safari, twitter, messages, various safari pages - MBP is sitting around 70-80c - nothing else is obviously spiking, these apps all using 1-10% cpu constantly - I have MX4 thermal paste on this MBP recently done so its not the physical thermals - after applying that I got much lower than previous temps.
Activity monitor uses 7-10% cpu also when running as the main window.
EDIT: Using notepad to make notes uses 14% CPU - 'brave browser helper' jumped to 26% usage.
WEIRD !! Anything that's running seems to use abnormally high processing power all of a sudden?