For Mac? Man Ide really have to look. Would probably find it easier for PC. Been while since ive done any of that stuff. But all it is, is a program that runs in the background and records every key pressed to a text document. It's how a lot of viruses get your passwords.
As for a program that records percentage of use like a heat map? I'm not sure that exists. I know some RGB keyboards have a simple function kind of like that with the color of the keys some times though.
Edit... Quick Google search for PC. Warning though I have no idea if the softwate linked is safe or legit off hand. Just an example and the 1st thing I found.
The best free keylogger (the only free one that sends mobile notifications) - http://www.spyrix.com/spyrix-free-keylogger.php Good luck. As a first line of defense, you could try the BSOD prank https://www.screensaversplanet.com/screensavers/blue-screen-of-death-222/ Before they have a chance to figure that out, the keylogger will have already sent you the notification, and you can call them and mess with their head for a while, like maybe tell them to go in your room and see if your PC was left on, because it's sending you strange messages, and pictures.