I think you do not understand how it works. Hardfork does not alter the maximum supply of bitcoin, it just creates an altcoin based on the current blockchain. But bitcoin will still have 21M maximum supply. If ever the hardforked coin survives, it is just an altcoin and will compete with bitcoin on the market.
bitcoin is indeed made by the creator of satoshi nakamoto for only 21M, but the value of bitcoin will still be this altcoin reference so that the value of bitcoin will forever be higher than altcoin, maybe bitcoin in the future can be like diamond because the number is very limited and everyone wants to have it,