NGINX Proxy Manager and DuckDNS.

Get DuckDNS set up first.

Then go to DuckDNS.org and register a domain.

Then go into NGINX proxy manager.

It's pretty straightforward, click "add proxy host", then type the domain from duckdns (I like to do a different subdomain for each service, ie: calibre.mydomain.duckdns.org, homeassistant.mydomain.duckdns.org, etc.) and point it at your container with the service you want to access remotely.

You'll want to enable let's encrypt. But other than that the defaults should be fine.