To answer the original question, voters have a right to be upset about inflation even if it's a global problem. The US leads the world economy and our leaders deserve some of the blame even for global problems.
Did Harris not explain the problem well enough? She did not. Neither did you, for what that's worth. Democrats tried denying it. That didn't work. Then they tried, "not really our fault, global problem" like you did. That didn't work either. Here we are. But that doesn't mean there was no way for Democrats to win, because the voters weren't actually asking what caused the inflation.
They didn't want Harris or Trump to offer them a macroeconomics lesson. They wanted a plan, or a concept of a plan, to improve that in the future. The voters were expecting Democrats to acknowledge their role in the thing and recommend a different policy path.
Harris was on the right track with the "build more new homes" idea. But the rest of her statements on the economy badly missed the mark, either more of the same, or new ideas that wouldn't work.
Trump's ideas were bad too, but they were different at least. And his worst ideas weren't as bad as Harris's worst ideas.

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