After research, I found a solution for my problem. Before I joined the exams, I always made sure that the camera settings match the requirements (for example, that the screen of my laptop is clearly visible in the camera, or that my workplace is visible).
Unfortunately, I did not close my camera before joining the meeting. I found out that the camera can only work with one application at a time. Of course it cannot work on Zoom, if I have already opened it.
I can recommend to everyone to make sure that the camera is not running (also make sure to close apps that use the camera), before joining a Zoom meeting where the camera is required.

Camera is not found on Zoom?

I usually don't have any problems turning on my microphone or camera at Zoom. During an exam (right there, of course), I suddenly couldn't turn on my camera. When I tried to click on the corresponding sign, I was shown that no camera could be found? This problem was so strange that I didn't know how it happened and how to solve it. Finally, I joined the meeting with a second device, on which, fortunately, the camera worked. In later meetings the camera worked normally again. This actually happened to me twice and only during exams, where I did not find the time to fix this issue.

I found out that by default, Zoom lets attendees change their own names during a meeting at any point. However, sometimes this option seems to be missing. The reason for this is that Zoom has a setting that lets Hosts choose whether they would like to allow the attendees of a meeting to be able to change their name once a meeting has started.
I found this information here:

There are several ways to solve this problem. The easiest way is probably to ask the meeting host to enable the setting, that allows participants to change the name. I solved the problem by leaving the meeting, logging into the Zoom app, changing the name there, and then rejoining the meeting. It would have been much easier to just ask the host to change this setting. Fortunately, I was able to rejoin the meeting fairly soon, so I didn't miss any part of the lecture.

Cannot change my name on Zoom

After joining a Zoom meeting, I noticed that I can't easily change my name. Normally, there is an option to change my name by going to "All Attendees" and hovering over my name. However, for some reason, this option was not available during a lecture.

Online timetable management

With calendar software it is easily possible to manage timetables of many people. Simple login and occupying time information is enough to manage meeting times.
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