Networking noob here. I want to prevent all incoming requests except through a specific port, and that traffic is forwarded to a specific device on the network. NAT seems to do that just fine, it’s almost like a kind of firewall by itself. What kind of threats are there that requires more than just NAT for security?
There are several ways to evade NAT. Your router may or may not block those, on a case by case decision. You must know really well how it will behave to have any confidence that you are secure.
Or, in other words, NAT isn’t a security feature because it’s not built to provide security. It may be intentionally broken so your home network works better, and it may have obvious security flaws that nobody looked after. For network security, you should use something intended to give you network security.