I personally think that the main problem is bad search optimization. There quite a lot of good answers on Fediverse (Lemmy) but it is nearly impossible to find them via Google or any other regular search engine. And making things worse since Lemmy is Federated it is not easy to implement correct indexing for it. So it makes a lot of questions(Should each instance index only local posts to prevent duplicated search results? What about small instances? Or use some central instance like Lemmy.World? What about different frontends for same instance like Photon or Alexandrite?).

Also Lemmy posts aren’t displayed correctly on Mastodon

I thought XMPP compatible with ActivityHub. Then I need something else

It is like what I need. I registered on conversations.im but can’t access neither my account nor created channel from Mastodon. How to fix this?

Seems like this is the only way. But if I want to create many accounts I need have several emails or self-host own instance.

Try to rephrase the question: is there an alternative to Mastadon in Fediverse where you can write posts in different threads (not only in your own feed)?

Lemmy is not that I need. Mastodon satisfies my needs more but I cannot create topics, unfortunately

It is too powerful for small messages posting

I need channel to be visible in Fediverse.

I can just create several Mastodon accounts and use each for separate topic bit it is not very comfortable.

It seems what I need but it is incompatible with ActivityHub, so cannot be followed or viewed in Fediverse (Mastodon)

No, in Lemmy communities everyone can post messages, and discuss.

I can just create several Mastodon accounts and use each for separate topic bit it is not very comfortable.

Discord and Matrix is more messangers and “groups chats” when Telegram Channels similar to Mastodon but with specific topic