So, really, you were "correcting" me for you and your specific setup at the very beginning because your router's firewall has a deny rule for all inbound connections because I must have been confusing what a NAT and what a firewall is because I must have been talking about your specific configuration on your specific devices.
Oh come on, are you seriously suggesting that default-deny stateful firewall is not the norm??
Holy. Fucking. Shit. Indeed.
You keep on suggesting to me that you really have no idea how networking works. (Which is par on course for people thinking NAT == security, but I digress)
Let me tell you: All. Modern. Routers. include a stateful firewall. If it supports NAT, it must support stateful firewalling. To Linux at least, NAT is just a special kind of firewall rule called masquerade. Disregarding routers, even your computer whether Linux (netfilter) or Windows (Windows Firewall) comes built-in with a stateful firewall.