I was just thinking about the time when all BTC will be mined. I know we all won't live at that time but I'm wondering... If the fees should cover the cost of mining, won't they be too high?
Too high for buying cup of coffee? Maybe. But you need to think also how worthless everything will be in 2140 in fiat money. 120 years of more endless inflation IF the fiat even survives that long.
But to answer your question: Smaller purchases will be made in Layer 2 tech like Lightning network and those payments will be "saved" in the Layer 1 blockchain only at the end of a day or a week. So it is not a problem.