I don't think you can "avoid" inflation in fiat. It's an integral part of debt-based money. Governments just try to keep inflation somewhat under control when they can, so that it doesn't rise too quickly. Usually not with any great deal of success, but that's the theory, at least.
You technically could if there was a finite supply of fiat. A currency based on the gold standard wouldn't have any inflation, granted the supply of gold was steady. Even without a gold standard, a fiat currency based on magic pixie dust could theoretically not have any inflation, as long as the government is unwilling to create more supply.
Government targets the inflation rate to be at 2 percent, so they'll make adjustments accordingly. The problems arise when you try to increase the money supply too rapidly, like the US does by having a debt balance sheet of trillions of dollars -- predictable result is an insane 7 percent inflation rate (compounded by COVID, of course).
You can perfectly avoid inflation in fiat and it does not need to have a limited supply. It is a simple as printing money based on the real growth of the economy so that the monetary mass is in sync with the real demand for money. To explain it for a 9 year old: You print the money that is required. If you print less, there is deflation, if you print more there is inflation.
Bitcoin is NOT inherently deflationary.
The central banks purposely target inflation to be at 2 percent, so even in a perfect world the money supply coincided perfectly with GDP, it'd be difficult to pull off. You're one economic dip away from ruining the entire system before the central banks panic and begin injecting money into the economy to save industries that would have probably crashed had it not been for intervention. Just use COVID as an example, debt of most countries began to sky rocket. The US in particular has their inflation rate out of control so it isn't merely just a problem with supply chains.
That's the issue with centralized economics, the entity in control inevitably loses control.