What are you all doing with your installs.
Literally never happened to me. Not in 1809, 1903, 1909, 20H1, 20H2, 21H1 ever.
It surely did some stuff believing it was idling while I was just surfing on my phone but it never restarted from itself. And I manage a good amount of PCs (Win 10/11 Pro) to say this is not a thing. At least not in Germany.