Apple - Can an iPhone 7 be made to function as a NFC Tag?

The iPhone is perfectly capable of this, but this is a privilege Apple keeps to themselves.

If you're jailbroken, you can install NFCWriter X and do pretty much everything you've asked for. I haven't personally checked, but I would strongly assume this is the exact same way Apple Pay works as well. So the iPhone is certainly capable of this.

The problem is that apps are not capable of this, because Apple denies them the availability of such an API. The CoreNFC framework only allows reading, and the story has gone so far as that organizations have sought fully third-party access to the iPhone's NFC chip on a legal basis. They were dismissed however, with Apple Pay keeping its uniquely privileged status.

No. iPhone can function only as a NFC reader. It is not possible to use it as a NFC Tag, and read it via some external NFC reader.

NFC is available in iPhone 6/6 Plus/6s/6s Plus/SE and NFC with reader mode is available in iPhone 7 and later.