ln: /usr: hard link not allowed for directory

Also Lemmy posts aren’t displayed correctly on Mastodon

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 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