Oh, that UI paradigm already exist. It's just that browser makers are too busy with things like webasm, webgpu, or allowing pages to launch location/notification popups at users, so they don't have time to fix fundamental flaws.
Alternatively, we could disable clicking/selecting anything that wasn't visible for at least 200 or 300 ms at that location. So if you try to click on a button and it's shifted down or something pops up in front, and you end up clicking on that instead, your cursor would just blink red.