Surely they aren't covering up that many deaths right? The US is 4% of the world population, and represents 16% of the fatalities. If China had our rate of fatalities that would indicate that they are hiding 4.3 million deaths somehow.

Last year the Economist estimated them at about 1.7 million excess mortality. There is extremely strong pressure from the top down to minimize the public death count. The credibility of the party (and Xi personally) relies on their Zero Covid policy being seen as effective. I wouldn't even call it a cover up, there are just no incentives to accurately report and many reasons to downplay aggressively.

Why wouldn't they? It's not like they aren't used to covering up deaths