Doing studies on this is difficult for many reasons. However, I bet there's a lot of people who noticed a drop in productivity from certain colleagues after the switch to WFH. I personally noticed that the productivity of colleagues with young children dropped significantly, for example.

I really don't think it's a controversial statement that some people work better from home and some people work worse from home. In fact, I'd be extremely surprised if the opposite was true (everyone works better from home, or everyone works better in the office), I'd almost say that's impossible.

I think you misunderstand me.

I think some people _are_ more productive WFH. But also there are lots of people who become quite unproductive WFH. Direct managers can often tell.

I don't know of a study that says one way or another, but from experience those two kinds of people exist (among other kids of people).