You can register #XMPP account for free on xmpp.social for example.
However, my consideration is to also offer a #Mastodon installation on this domain (or something else for the social web).
Problem is: either you will have two separate accounts or I need to move the existing accounts over to my LDAP server and connect both services via LDAP.
Separated accounts will have the challenge to prevent that two persons register the same nick on both sides.
What would you prefer?