This is the chart of Bitcoin's Avg. Transaction fee:
https://bitinfocharts.com/comparison/bitcoin-transactionfees.htmlRight now the median fee is about $2. After lots of halvings the reward won't be enough to satisfy the miners. I guess that after a decade, bitcoin will be more widespread, as a result, more transactions will occur every second. Won't this increase the median fee? If it does, bitcoin will start being a not-so medium of exchange. Imagine paying $5 for a transaction. Even paypal doesn't charge that much.
The next block reward halving is almost 4 years away, so that is not an immediate concern for the miners. BTW, you need to understand that the userbase is expected to increase sharply in the future. Along with it, the number of transactions may also witness a steep surge. So the fee reward per block may remain stable, or even show an increase. But the median transaction fee will remain at the same level. The only thing to remember here is that we need a substantial block size increase at some point in the future, to keep mempool at tolerable levels.
https://mempool.space/