Like many other popular weird physics effects, it has been accepted non-controversially by scientists and then popularized for decades in fun thought experiments and pop-sci videos, all of which neglecting to mention that no actual experiments have yet been performed. This lack of grounding leads to spread of confusing statements like "the Unruh particles exist in the accelerated frame but not in the lab frame", which make no sense, for how can there be two separate realities that coexist? Luckily we now do have a first Unruh experiment from 2019 https://arxiv.org/abs/1903.00043v7 and the temperature did rise and reality did not split apart. So no longer hypothetical, just routine and boring.