Not sure if my setup is unique or wrong but here’s what I use:

1. I registered a domain with Name cheap and created subdomains for the tools I wanted to access (i.e. jellyfin.domain.tld, sonarr.domain.tld)
2. A DDNS client on my OpenWRT router updates the IP address for those subdomains. Traffic for each subdomain is pointed at my server.
3. Nginx Reverse Proxy runs on my server. This provides HTTPS certificates and is pretty straightforward.

Why don’t we need this for Plex? Because Plex has all of the above steps baked into its service.