The warm-up is a great way to bring everyone into an online meeting. However, I would suggest that everyone has tested their microphones and video BEFORE the meeting starts.
The warm-up needs a little more management online. The question or idea that is the warmup subject can be delivered as usual, but nobody will know when they should speak, so I suggest the participants’ list is taken as the source of attendees and you work down the list one by one. You will need to introduce each person by name as they won’t be following your process.
You will also find that many people are not so good on time when online, so your timekeeper needs to be strict and make an appropriate sound to stop those going over time.
If they don’t stop then a firm but fair mute of their microphone could be in order.