One wonders what the manager is doing so that they are in a position to just be “watching other people work” 🙂

The only thing that I’ve heard is that sometimes there are groups where people like to have videos of each other running, as a kind of simulation of being in an office together. I think for me I’d either find it very distracting, or I’d quickly tune it out.

I think your putative manager should focus more on output than on whether people are making “I am concentrating” expressions to their webcams 🙂