R_Kasatkin said:
there are groups on FB, Linkedin etc.

what do such communities look like? are there any examples?

You said there are groups. And you ask what they “look like”? You need examples of these groups that you say exist?

Maybe you need to clarify your question. And have you looked at those FB and LI groups to see them for yourself?

R_Kasatkin said:
And they are quite active there. And what do such communities look like? are there any examples? how to search? And, can you advise someone who has studied this issue?

This is the issue with discord and other closed communities. As far as I know, they currently can not be searched, categorized or found in an easy way, You'd have to join them individually to see what they are about. I don't even think admins have access to the kind of data your looking for. It sounds like your looking for marketing reasons and other related research purposes? That break down user activity?

Most of these platforms have what I call “a fire and forget” method of communication, meaning every individual user posts content expecting others to read it, when a large majority of activity is backlogged and glossed over by the average fellow user. Most people don't scroll to read chat histories, unless they are looking for specific content.

Each community is restricted and defined by its medium.

A Discord group will look different from a fb group. Lumping and cross comparing communities across platforms may be tempting, but it won't capture the essence and complexity of each community.

You say “we” so what are you people looking for specifically? what is the target or goal?

I don't even think these platforms offer tools to aggregate data for marketing purposes.