Long story short, if there's no critical radical change to BTC's structure then miners will rely solely on fees and the existing BTC will start to deflate as money is lost various ways. The "lost" BTC is already much more than many think, which makes the BTC maximum supply even smaller than 21M (which was a low amount already anyway).

But the year all BTC will be mined is too far away to talk about it now. Lots of things about Bitcoin and crypto in general have changed since 2009 - the world is in a big change itself. By the year BTC touches its max supply, I would personally bet there'll be some hard fork to add more zeros before the dot or the fees might become too high to be affordable.

Until then, it's mostly speculation but there might be a core change. There's a possibility that Bitcoin will fail long before all coins are mined.