Once all bitcoins are mined, no new supply will enter the market and availability will depend on people trading existing bitcoin. This scarcity could increase demand and pushes prices higher but it might also make bitcoin less practical for smaller transactions if prices become too high.

You can check this article: https://www.ccn.com/education/what-happens-to-bitcoin-after-all-21-million-are-mined/#:~:text=By%202140%2C%20all%2021%20million,rely%20solely%20on%20transaction%20fees.