Unraid isn't designed to have an outward facing webui, it's not hardened for it and although it's possible (at least with nginx - I played around to see how to do it on a VM) it's very much not recommended.
Whilst the advice you have received may not be what you hoped to hear and obviously hasn't been well received, it is pretty sound advice nonetheless.
Got no experience with Caddy myself, so can't help you with your query, but I can only echo what others have said, which is that it isn't a great idea.
If someone does get access to your Unraid webui they essentially have root access on a server on your LAN. Not a situation you'd want to find yourself in to be honest.