As mentioned I was trying to watch Carl race, but it turned out to be impossible.
I could see that Carl was "Zwifting now" on my Phone. When I switched to details, there was only one "Ride on" button (it was probably me sending that during the race

).
I then started Zwift on my PC and chose to just watch, which took me to an random rider.
Then found Carl on the app, and now there were more buttons. Clicked the "Fan view" but noting happened. Clicked it again and it switched view to myself. From here on the button had no effect.
I then tried to re-logon to Zwift on my PC and join Carl. That was a bit bizarre. Apparently you can join a rider, even during a race (Carl, did you see me?), initiallly in "Pedal Assist" mode, but that is only for a short period. After that you have to ride normal.