Another option is an XMPP-based stack with Converse as webchat with either ejabberd or prosody as XMPP server.

https://snikket.org/service/quickstart/ (uses prosody)

https://docs.ejabberd.im/admin/configuration/modules/#mod_conversejs

https://wiki.debian.org/FreedomBox/Manual/ejabberd#FreedomBox_webclient

https://conversejs.org/docs/html/setup.html