I guess it depends on your setup, but for me, based on your role, you're automatically part of all the channels that are relevant to you. You can mute channels if they become distracting and aren't relevant. I find this way better, as when we get new people they are instantly part of everything they will care about. When we had slack, I found I had to force join people to channels because they wouldn't know to go particular channels.

I think it is possible to do this with roles and bot managing those. Ofc, that is not standard solution.