I don't mean to prescribe the way to stop fingerprinting, just throwing out a trivial existence proof, and maybe a starting point of thinking, that it's not impossible like was suggested.

Also, WebGPU seems to conceptually support software rendering ("fallback adapter"), where fixed time rendering would seem to be possible even without getting cooperation from HW drivers. Being slower than WebGL might still be an acceptable tradeoff at least if the alternative WebGL API avenue of fingerprinting could be plugged.