Indeed, Bitcoin Max supply is 21.000.000 BTC, to allow for a larger supply, the Bitcoin's protocol has to be changed.
For now, everything is OK and we are not facing any problems, but when all bitcoins are being mined many expect troubles.
Miners will be the first to be effected since there will be nomore block rewards and you can imagine the negative effects of miners quitting mining
due to low profitability. Consequently, the Bitcoin network will be more centralized.