There's an app for that, Fog of World.

Here's my map.

Its a nice idea , but I will hate the way these tech giants choose to implement it. 99% of implementation would need location to be tracked 24x7 and stored in their server . If someone would have a local or private way to do this , I'm exited.

I kind of do that but in reverse with Google Maps Timeline and Strava heat maps. I can see where I've been and where I haven't been so far.

I guess if someone has their location history something like this wouldn't be too hard to accomplish.