You are right to think about long term future of Bitcoin especially with its limited supply. And after all 21 million Bitcoins are mined around 2140 miners will still exist and will keep network secure and processing transactions but their income will come from transaction fees instead of newly created Bitcoin.
Their earnings will entirely be based on transaction fees, and the fees might likely get even higher than what we usually see in terms of these creators that do NFTs on the network and cause fee increases due to the congestion. Since the cost of mining is expensive, there will be a way for them to do it in order to meet up with the expenses.
These fees could become higher and new technologies like Lightning Network might help keep them manageable. Bitcoin price will continue to go up and down as it is doing at this time influenced by global economics and how widely it is used but daily trading should still be possible driven by its fixed supply and ongoing demand as valuable asset.
As long as the demand for bitcoin still continues and with institutional investors and government being involved, the price increase is more inevitable compared to how it has always been, as the supply for bitcoin is just too small compared to the demand for it, which is rapidly increasing as time goes on.