You can always sign up for the default matrix server and try it out there.

Personally, I think the video and screen sharing runs slow and janky, but it might be the closest thing to Teams or Slack especially if everyone is on the same network.

As far as I know, there are zero parents who signed a counter petition.

I’ve never heard of this organization before, but a quick look at their page demonstrates they aren’t just some American or European exceptionalist group. Which is good, because privacy and authoritarianism are two diametrically opposed ideologies that cut across nationality.