> What if our phones and computers had adequate ambient light sensing that the shadows can be Aligned to the environment?

That is an interesting concept. I suspect the only times it would work would be when you are sitting near a desk lamp or are outside in the sun (directional light from a points source). Otherwise you will likely have omnidirectional lighting.

You could use the accelerometer, which would either work like those dynamic backgrounds.

Personally I'm OK with "flat" stuff in predictable places like the macos menubar - all things in a constrained space are either drop-down menus, or are for information with clickable settings

But in free-form where anything can appear, always on shadows for buttons might be boring but they are GOOD.