Hi Lora_C,
Thanks for reaching out! I'm Nik, Independent Advisor here to help you with this case.
It looks that you had allowed participants to join the meeting without an organiser. In that case, the first participant get the organiser role in-spite even if he did not organised the meeting. Joining as organiser, allow him to end meeting, kick someone from ongoing meeting etc.
I would advise you to look meeting options for participant settings to ensure who can join the meeting directly.
please refer section - "Change participant settings" in the article - https://support.microsoft.com/en-us/office/chan...
Highlights, if you set "Who can bypass the lobby?" to "Only you" then As the meeting organizer, only you can get into your meeting directly. Everyone else will wait in the lobby.
I am sharing video walkthrough tutorial for more details:
https://youtu.be/uAG9W4x02x8
I hope this helps!
Regards
Nik