Andrea Veri commented:
Landed the missing www.gnome.org/.well-known/matrix/client file. This should fix the reported issue @thibaultamartin. Please keep going with the evaluation. As soon as a decision will be made on the final messaging tool of choice we'll discuss a proper migration plan against our infrastructure (to benefit from LDAP - GNOME Accounts - authentication) including a discussion around what to do in terms of Matrix IDs to use for guests and standard / regular contributors. Thanks!