Just because Owncast listens on port 8080 doesn’t mean your server has to accept connections to it on 8080. You can firewall this port if you like. Then you’d run Caddy on standard ports (80 and 443) and reverse proxy to localhost:8080 to connect to the upstream app from within the firewall.
Running it in Docker is also another way to configure things that would make port 8080 no longer a problem on the server.
The article linked by @Rob789 above:
is going to be very helpful to wrap your head around some of the important concepts. This will be necessary in order to formulate a plan for how your server host (the machine, either your own server hardware or the VPS), the service (Owncast), and the web server (Caddy) fit together; even if you don’t actually set it up within a home network, necessarily. I can’t recommend the article enough.
After reading through that, you can ask any questions you have here, and then you’ll want to start working on a Caddyfile. Once you’ve got something you can share we can go over it, discuss what you’re trying to achieve specifically, and help you get the rest of the way.