I would go as far as saying that Harbour-hydrogen is not developed anymore, and that almost goes for Sailtrix as well.
I raised this at a Community Meeting this spring: Community meeting on 26th March 2026 - #5 by frankps
My hope is that somebody contributes to Sailtrix or do a new client (hopefully a port of Element X or Fluffychat). Another great option would be if Jolla implemented Chatty as a replacement of Telepathy: https://gitlab.gnome.org/World/Chatty
SFOS needs updated chat clients for Mattermost, XMPP, Nextcloud Talk and Matrix.