When prices increase we pay more for goods and services. Cost of living is higher because of inflation—we have to work more to earn enough money to buy the same goods and services. Who is at the other end of that transaction? Who is it that gets paid more for the same goods and services? Until everyones gets a raise so they can work the same number of hours to afford life as before inflation, someone is profiting. Who is that?
One answer is “anyone whose assets in USD (and USD-equivalents) are negative”. For example, the U.S. federal government owes $31 trillion at the moment. If dollars become worth 5% less, then that’s like reducing the debt by $1.5 trillion.
People who are keeping their prices up to date gain little, while people whose prices were last negotiated awhile ago lose a little. But this effect is small, and slightly misses the point.
What inflation means, fundamentally, is that there is more money chasing less stuff. Or rather, the money-to-stuff ratio has shifted. That means either the amount of money going around has increased, or the amount of of stuff to buy with it has decreased.
Usually the amount of stuff-to-buy is increasing, since we keep building more and better factories and generally increasing GDP. So in the typical case, inflation means the amount of money in circulation is increasing even more than that. You can think of this as the government levying a tax on dollar-denominated accounts, equal to the amount of money printed. In the case of the US government, there are a bunch of extra steps involved, which mostly just serve to obfuscate this fact.
In some cases, though, inflation reflects a collapse in supply. Eg at the start of the Russia/Ukraine war, a bunch of trade was disrupted in ways that meant actual total production fell. Eg Russian natural gas exports to Europe stopped and the gas was flared off instead. In that case, no one is profiting off the inflation; there is simply a loss, and the shifting prices are simply part of the mechanism that determines who bears that loss.