What will happen after all the 21 million bitcoins have been mined?

When bitcoin was invented in 2009, it came with a hard cap of 21 million. This is the highest number of bitcoin that can ever be mined or supplied. Based on current mining rate, the final bitcoin would be mined around 2140. After 2140, no new bitcoins will be circulated or supplied.  At the time of writing this piece, only 2,208,000...