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.
Technicailly this is a pretty big issue. And I think we even had a lots of discussions about this in January 2018 when the fees suddenly skyrocketed and I remember the technology of lightning network was pretty popularized at that time and it was expected that it would solve lots of these issues related to scaling but the pace of development of this technology has been pretty slow and I think there have just been a bunch of use cases of this technology. Moreover it faced tremendous criticism for making the chain centralized which it technically didn't. But yes there would definitely be an issue in the future.
Some people have suggested that even the fiat mechanims like Paypal etc. charge a tremendous fees which in compared to bitcoin is higher but I think the ideology here shouldn't be to blame bitcoin or paypal for charging heavy fees rather creating a hybrid solution which could work out towards lower fees. A few other coins have evolved for this purpose but as usual turned out to be shitcoins at the end.