Whataboutism is a very useful game to reveal whether people are being honest or not.
If someone is vocally complaining about country A doing some oppressive activity, while ignoring country B doing 100x the same activity, the comparison does not forgive or excuse country A, or make them right or admirable.
But it does allow us to conclude that the person complaining is biased. Either they don't care about the oppressive activity and want to attack country A for some other reason. Or they have a particular fondness for country B and will never accept that it does wrong. Or some variation on these.
Except it’s op posting whataboutism not me - their claim is that China has done nothing wrong to them with the implication that the USA has. I was highlighting that China indeed likely has done the things they’re complaining about.