[michel-slm]

Which desktop client did you try? The official Mac client, at least, has secret chat just like the mobile clients (I just used it yesterday)

Note that Telegram secret chats are end to end encrypted (default chats are not) but you're still dealing with the Telegram server (not peer to peer)

[xstartup]

I tried arch linux one.

[narg]

I have just installed the Mac client and it allows to create new secret chat but it does not show the secret chats created before on your phone. At least that is what happened to me.