How do you want to connect the internet to your server? You mentioned ddns, have you enabled port forwarding (you mention fw rules but dunno if you mean port forwarding)? Have you check if your isp actually lets you do port forwarding? What ip addresses you use, v4 or v6? Have you ever gotten a connection from the outside world to your server? Forget https or domain resolution for now, can you connect to it somehow?
How do you want to connect the internet to your server? You mentioned ddns, have you enabled port forwarding (you mention fw rules but dunno if you mean port forwarding)? Have you check if your isp actually lets you do port forwarding? What ip addresses you use, v4 or v6? Have you ever gotten a connection from the outside world to your server? Forget https or domain resolution for now, can you connect to it somehow?