@SrGuspin So, if understand correctly, you are able to port forward to Nginx Proxy Manager just fine, but you can’t get the SSL certificates to work, so you are connecting a Cloudflare Tunnel to Nginx Proxy Manager and then relying on the SSL certificate from Cloudflare?
How did you try to generate the SSL certificate on NPM? Was it through your domain registrar (like I showed with Dynu)? Also, are you able to verify that you have correctly set up port forwarding for your network and DNS records for your domain so that your network can be reached from the outside?
My first hunch would be that your network is failing to communicate with your domain and/or the internet in general, which would explain the failure to generate an SSL certificate and suggest a possible port forwarding issue. Cloudflare Tunnels would, of course, circumvent this issue as they don’t require port forwarding.