An NFT is a digital token that is unique in a collection of similar tokens. Its uniqueness makes it a standalone asset that is valuable, resellable and transferrable. Fungibility refers to the ability of an asset to be exchanged with another without value being lost. Bitcoin is a good example of a fungible asset; you exchange fiat currency for btc and viceversa but no value is created in the process. Its just conversion of currency from fiat form to digital form or the other way round. It's forex. No matter what terms are used-digital gold, safe haven money or fast money-its all basically finding pairs of fiat/crypto, crypto/fiat and crypto/crypto that are profitable and betting on them.
NFTs are different. Non-fungible assets can't be just exchanged with one another. They can't be barter-traded. A comparable real-life example is exchanging an orange with a book. Irregardless of their respective cost, those two can never be equal. If random people were asked to pick from the two, they will all pick either and have different reasons for it. This difference in preference is where value arises in NFTs. That coupled with digital scarcity and security make NFTs viable digital collectibles.