the total supply of bitcoin is less than 21 million bitcoins (21 million is a rounded number) and when the block rewards halved to very small amount, the mining rewards to confirm transactions might be bigger than block rewards. We never know what will happen with bitcoin network, its transaction fee (in satoshi units or in USD value) in next one century. Miners leave the network, total hashrates fall down, more developments for other layers, many things can happen in next one century.
Some explanations on bitcoin total supply.
The supply will approach, but never reach, ₿21 million. Issuance will permanently halt c. 2140 at ₿20,999,999.9769.[6][7]:ch. 8
The protocol also halves the rate at which new bitcoin is created every 4 years, and limits the total number of bitcoin that will be created to a fixed total just below 21 million coins. The result is that the number of bitcoin in circulation closely follows an easily predictable curve that approaches 21 million by the year 2140.