Just installed TigerVNC 1.14.1 from staging and it fixed the problem! Release notes of the version list
Default installation of native viewer can once again handle VncAuth
which could explain the behaviour.
Remmina shows
(org.remmina.Remmina:308321): remmina-DEBUG: 12:08:09.441: (remmina_plugin_vnc_rfb_output) - VNC returned: ConnectClientToTcpAddr6: connect
(org.remmina.Remmina:308321): remmina-DEBUG: 12:08:09.441: (remmina_plugin_vnc_rfb_output) - VNC returned: Unable to connect to VNC server
which does not make much sense because the IP is IPv4, but it works if provided on commandline using the protocol syntax:
remmina -c vnc://host:0
Thanks everyone for your help.