This will stop people from joining the meeting immediately, and will prompt the meeting admin to let them in.
In your meet that you have admin controls of, click on the blue shield in the bottom left.
Turn off the Quick Access toggle.
Now, when people try and join the meeting, it will prompt you similiar to the below. You would press Admit to let them in.
And they will see this, until you admit or deny them.
If there are any questions or issues please contact IT Services