Some argue that it is an asset but their explanations does not convince me. Now I ask, what is bitcoin if it is not cash?
What explanation of what Bitcoin is convinced you? That is exactly what it is to you.
There is no fixed use case for Bitcoin, people use it for different purposes as it suits their needs; It can be a store of value or a means of payment or a a tradable asset.
Now I ask, what is bitcoin if it is not cash?
Cash is liquid money, such as notes in your wallet. Bitcoin is definitely not that as it is digital. If by 'cash' you meant fiat, Bitcoin is definitely not that too as it is decentralized.