Since BTC is a decentralized currency over the years now, is fungible because there are some coins in the market you can buy and hodl, and they will give you profits BTC use to give to those that invested in BTC, and if BTC disappear from the market today there will be other coins people can use to replace BTC investment in the community.
You are missing the point here. BTC isn't fungible because it can be replaced with another coin in the future, that is not it, because they would never be of the same value. BTC is fungible because it can be be replaced with another asset of equal value, i.e. if i borrow you 1 BTC, i do not need you to return exactly the 1 BTC i borrowed to you, you can return a different utxo to me as long as it is worth 1 BTC, or you could even give me 0.5 BTC twice, which makes up one BTC, that is the fungibility we are talking about.