Personally I think whataboutism to excuse bad behavior is awful, but using it to criticize an accuser's hypocrisy or double-standard is fair and legitimate.

For instance, the event with Evo Morales' plane being forced down in Switzerland, while not exactly the same, clearly set a bad precedent and we're paying the price now. I don't have any problem with saying that what Belarus just did and what happened then with Evo Morales' plane were both wrong. (At the same time I support European countries sanctioning Belarus even if they were the same countries that just a few years ago denied their airspace to Morale's plane for political reasons.)

https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident