As long as you have a meeting ID, you can join and cancel virtually all video calls on Zoom. And that's how we get terms like "Zoom Bombing", where someone jumps into a chat to say or visually show vulgar and inappropriate things to the other participants. But hosts can put a stop to it.
Zoom bombing happens more often than you might think. Zoom calls around the world have been shortened due to harassment, pornography, violent images and trolling. Chipotle, WFH Happy Hour, USC and the Department of Defense had to shut down Zoom meetings, and countless students were exposed to the problem.
To combat Zoom trolls, the company recommends that you do not use your Personal Meeting ID (PMI) for public events because it is a link you will use again and again. It also recommends that you use the Waiting Room feature for all video conferencing that you host, so you can control who comes and goes and lock meetings when everyone who is there is present.
As a Zoom host, the most important thing you can do to prevent unwanted people from ruining your video calls is to control who can use their microphones, cameras, and screen sharing capabilities. For screen sharing attacks, it's easy on your iPhone or Android phone to control who can share content.
Note that disabling sharing in your current meeting will not disable it in the future, so you will have to redo the steps each time. And even if you can disable the microphone and video for the participants individually, you can only kill sharing for everyone except yourself, the host.
When you have started a zoom meeting, click "More" in the navigation bar, then press "Meeting Settings." Find the "Allow participants to share" option and turn it off. It will prevent all participants, except yourself, from sharing their screen, photos and other content. You can switch again when needed.
When you have started a zoom meeting, click "More" in the navigation bar and then tap "Meeting settings." Next, find "Lock Share" and turn it on. Why the setting is called something else on Android is a guess, but the results are the same. It will prevent all participants, except yourself, from sharing their screen, photos and other content. You can switch again when needed.