What that does is allow existing outgoing connections through a NAT to remain open long-term, it doesn't actually help with establishing an initial connection if both sides are behind a NAT or closed firewall.

Tailscale handles this, and can establish a direct connection between two machines without either of them needing an open port listening for new connections.

There's an article on their website that explains how they do it: https://tailscale.com/blog/how-nat-traversal-works