The 120Hz shadertoy works on the Pixel 8 (and hopefully other 120Hz Android devices) if you go to Developer Options and enable "Force peak refresh rate"
I wonder if there's a way to ask Android Chrome to ask for 120Hz.
Ah, the non-developer option setting to enable 120Hz on later Pixels is under "Settings"->"Display & touch"->"Smooth display". With that enabled, Chrome will use 120Hz if power and temperature settings permit it to.
I wonder if there's a way to ask Android Chrome to ask for 120Hz.