The ESR MagMouse is being trailed on Kickstarter as the world's first magnetically attachable mouse and, well, I've never seen one before. I can now confirm that, having already been designed and now hit its target, it's definitely something you'll be able to get.
How do I know all this? ESR has let me test an early model, and so I've followed the instructions and stuck it to my laptop's screen. I can't say that it's done Apple's carefully crafted aesthetics any favors, but on the other hand there is no evidence – as I type this – of weird coloring on the screen side of the 2019 MacBook Pro.
