20% of meeting participants are only given the option of joining via audio and not video

We have had two meetings in the last month of 50-80 invitees but there are a proportion of the participants that were not allowed to have video and could only join via audio. They can’t see the shared screen or the chat box. I cannot see why this is. There does not seem to be a pattern ie local/overseas.
We want to limit the content of our meetings being captured and I am not sure if this is happening because we tick the boxes that prohibit screengrab/notes/transcript recording etc. There are so many settings now and I cannot find one that states a limit to how people can participate in the meeting.

Some people reported that when they joined via the app rather than browser it did let them have video after a couple of times rejoining the meeting, but this didn’t work for all. Some peoples’ workplaces do not let them download the app and have restrictions. We have had many big meetings in the past with the same cohort, and this has never been an issue before. Any assistance greatly appreciated.