The Adaptive Timeout feature that I discovered back in April is here in Android 15 Beta 3, at least on my Pixel 8 Pro! It doesn't seem to work for me, though.

Adaptive Timeout "automatically turns off your screen if you're not using your device."

UPDATE: Okay, I think I figured out how Adaptive Timeout works: It checks your proximity sensor to see if anything is in front of it (like the inside of your pocket). If so, it shortens the screen timeout and turns the screen off early.

This'll be useful for people who like to have longer screen timeouts but who forget to turn the screen off manually.