When you start the first Pomodoro, all you do is just start the timer, invite everyone to mute themselves.
I always make cameras optional for people, but personally I like having my camera on and being able to see people, but totally optional, totally fine.
Tell everyone to mute themselves and that you'll let them know when it's time for a quick stretch break.
Yes, people can see the timer, but you know, when you get into hyper focus, you're not paying attention to the timer. And stretching every little while is a good idea.
When the timer runs out on the pom, all you're gonna do is just bring yourself off mute and then quietly and gently say, "Okay, that's time on our first pomodoro," or something to that effect.
Since people have been in their own little universe and possibly in silence, be quiet and gentle. I've accidentally startled people before and it was really funny.
Then don't forget to start the timer again for 5 minutes before doing anything else.
Ask people how they're doing. I always got a vibe check at the mini breaks. Most of the time people would not come off mute, but sometimes they would.
And sometimes we would do some chit chat. But just encourage people to stretch, take a break, go to the bathroom, reheat their tea, or there might be something here that people need to do that's relevant to your theme.
I would often take like dance breaks or shake it out breaks and actually in front of the camera, shake it out. And that would get people moving too, so that was fun.
When the timer runs out, just say, "Okay, that's the end of our break, let's get back to it," or something to that effect.