Get a load of this handy little tool design from Lee Valley & veritas. It’s called the Brush lugg and it helps you open paint cans, but also can be either clipped or magnetized to them such that they provide a handy place to put your brush when not in use via another inclined magnet. They even have design consideration factoring in the fill level of the can in question. Wonderful design work here.
My mom got one of these for Christmas, still hasn’t uses it despite doing several painting jobs around the house.