For instance, with masks, the first months of COVID we heard almost every major government institution in the West parroting the WHO line: there's no evidence masks work.
Now, there were a couple problems with this claim. First, there was a sort of evidence: it had been used to great efficacy by Asian countries for decades, and then there's the basic mechanics of the thing—we know how flus and colds and similar viruses spread; the symptoms are the means of transmission that the virus establishes. Coughing, sneezing—the particles spread from my lungs into yours. Common sense and historical precedent were on the side of mask-wearing.
But these were disregarded—specifically, the claim "masks don't work" was built off the argument that there had been no studies of mask-wearing's efficacy stopping COVID's spread specifically. Nevermind the basic scientific error that absence of evidence is not evidence of absence. Nevermind they hadn't even yet gone looking for evidence, nevermind that the rigorous scientific work needed to establish mask efficacy w/r/t COVID would either be ethically impermissible (you'd have to run a study exposing humans to the virus with and without masks) or else require large statistical samples over time (i.e. we'd have to wait and compare countries/regions' rates with and without masks). So the kind of "evidence" the WHO desired was basically impossible to get.
The common sense + historical precedent should've been enough while we waited on more rigorous studies, but there was a political agenda: mask supply was limited, and governments wanted to make sure it stayed in the hands of emergency workers. That's pretty reasonable! But look how that "ought" ended up smuggled into a "scientific" "is"—it wasn't just that we should refrain from buying masks, it was that they didn't work. (Nevermind the incoherence of arguing emergency workers needed masks for protection, but masks offered no protection.) Suddenly there's a regime of liberals going around calling anyone wearing a mask paranoid, or shouting at them in bodegas about their "alt facts" and conspiracies. These liberals, too, believed they were on the side of "the facts"—only to reverse course as soon as the official government line changed.
Also important to remember: The director of the WHO is Ethiopian. Chinese and Ethiopian relations are so established they have their own Wikipedia page. China is well-documented as funneling massive amounts of money into the third-world to get UN members to vote their way. This doesn't necessarily mean that the WHO downplayed COVID because of Chinese influence, but it's certainly grounds for suspicions, and a reminder of the Foucauldian role of power in determining "truth."
What we have is a perfect illustration of the idea, which reaches back to and beyond Nietzsche, but is expressed most thoroughly by post-structuralist thought, that "truth and power are two sides of the same coin."
Your naive liberal view of "science", Tea, is not the one found in the halls of science—it's the one found in the halls of government, echoed by technocrats whose job it is to control the populace.