As I've explained to many, "whataboutism" is the strawman of legitimate "tu quo que' argument fallacy. Simply put it's a means of promoting doublespeak mentality, when in reality whataboutism isn't a thing. The examples labeled such can either be described as legit tu quo que(and should just be called that) or the valid argumentative notion known as precedence. In most uses it's the latter and promotes the aforementioned doublespeak.

In summary, calling anything whataboutism is never appropriate. It's just a creation of the left to stifle critical thinking.

Edit: Forgot to mention the one other use. If two people are talking about rising sea levels and one ask, "What about purple rhinos?" No, not whataboutism either. That's just simply changing the subject.