Support for ALPN has been added in PR #8913. However, it does not include ALPN types 'xmpp-client' and 'xmpp-server'. It has been requested before and my understanding was that it has also been implemented already. However, upon testing, I came to the conclusion that it does not work yet. Here are all the ALPN protocols including 'xmpp-client' and 'xmpp-server'
I want to use ALPN(xmpp-client) and ALPN(xmpp-server) as to route the correct traffic to the correct container (xmpp server container). As these ALPN protocols are not supported, I can't multiplex on 443 main domain. It has nothing to do with letsencrypt certificate requests. Certificates are manually loaded into traefik and also for the service (xmpp server). As described here and here, the server should set hostsni and ALPN to correctly use xmpp over tls (443).