The author admits that his criticism would fall apart as hypocritical if the West did similar things

That's false, though.

The West committing an injustice doesn't entitle China to commit the same injustice or another.

"Whataboutism" isn't even a real thing

Someone relying on whataboutisms to deflect attention away from the misdeeds of their favorite tyrants WOULD say that, yes.

Whataboutism is a real thing and that real thing is a logical fallacy of avoidance of accountability via deflection.

Random internet people just started saying it one day

Nope. That's grade A horseshit.

The term originated in 1970s Northern Ireland:

1974 letter by history teacher Sean O'Conaill which was published in The Irish Times where he complained about "the Whatabouts", people who defended the IRA by pointing out supposed wrongdoings of their enemy

Hardly "random internet people

but it has no logical basis

That's the thing: logical is exactly what pointing a whataboutism is.

It's a tu quoque fallacy used to manipulate the conversation away from a place that makes you uncomfortable by changing the subject to something you're more comfortable talking about, but which doesn't justify the thing you're trying to defend.

When looking at criticism of a particular country, obviously it's relevant whether other countries are doing similar things while only one country gets singled out for it.

Not relevant to whether or not the particular country is wrong in doing so.

If I was on trial for embezzlement, tax fraud, and defrauding a charity, pointing out that Donald Trump has done all of those things would not be a viable legal defense.

For the sake of clarity, would you mind answering whether every government that has ever existed is "tyrannical" by your standards

Nope, that would require me to take it as a given that your ridiculous strawman argument has merit.

whether you think China is in some way exceptional based on something relavent to the article posted?

This law, which is a Chinese law, is exceptionally oppressive against Uyghurs, Tibetans, Chinese people who speak any of the 9 other Chinese language groups that aren't Mandarin, and rightfully criticize the Chinese government for anything ever.

The above paragraph is true whether or not any Western nation has passed any similarly oppressive laws.

As for your "singling out" claim, it's an article about a specific law that's recently passed and currently being enacted.

That's not singling out, that's reporting on current events.