That did the trick. Thanks @jok! My working Caddyfile code block is:
# Nextcloud in a Docker Container
cloud5.udance.com.au {
encode gzip
import dnschallenge
reverse_proxy http://10.1.1.18:8000
redir /.well-known/carddav /remote.php/carddav 301
redir /.well-known/caldav /remote.php/caldav 301
}
Yes, I’m aware of the HSTS issue, but as I’m currently experimenting with various scenarios by building and pulling down Nextcloud instances, I’m happy to let that slip by for the moment.