I’m not sure if this will help you out since I’m really not sure what your problems are other than getting the reverse proxy to work. So, I’ll give you what I’ve found to work and if it’s not what you were looking for then you can just skip over what I"m yammering on about.

The process:

Spin up a container, let’s say it’s Dozzle and it needs port 1124. Container deployed, so lets put it in reverse proxy:

Issue command together:

sudo nano /etc/caddy/Caddyfile
sudo systemctl restart caddy	

Enter the following in the Caddyfile:

dozzle.myverycooldomain.duckdns.org:443 {
	reverse_proxy localhost:1124
}

Press ctrl x, press y, press enter, and the Caddy server restarts if you indeed issued the commands together. Now go to dozzle.myverycooldomain.duckdns.org for test run.