I also do an online class and unlike my colleagues, I don't have a dog to walk, spent months abroad before covid, had a new kitchen, or children who are doctors etc, etc. I therefore only join the group a few minutes before the class starts and just listen to the tail end of the conversations. I then have a few minutes general chat with whoever I am put in a group with. It works for me and is much the same as you mentioning that they all say they have been exercising. You just do what works for you and you enjoy what you do.
Schellea of Fabulous 50 on Youtube released a video a couple of days ago about how not to feel envious of others. Her message is that if you fill your head with thoughts about other people there is no room left for thoughts about yourself so let the other people go. I guess that takes practice but she is spot on.