it seems I’m missing something. I have installed jitsi “out-of-the-box”, everything left to defaults.
When a user changes the video quality setting in the client, this has absolutely no effect on the bandwidth. Also, the “icon” always says “HD”. Do I have to configure something? I found the section video:/resolution: in config.js. Assuming that what is given in comments there, are the defaults, it should be possible to adjust values between 240 and 720.