I don't rule out the possibility that COVID made some people think further on how they interact with software, and that indirectly promoted some Linux usage. However, I don't think that it would create continuous pressure encouraging adoption, that keeps going on four years later.

Another reason why I don't think that COVID is the cause is the timing: the "bulk" of the social impact happened in early 2020, but the slope seems to start near the end of 2020, almost early 2021.