The US has been deeply hypocritical by opposing the ICC, for example. But the policy fixes that we need for what's happening in Xinjiang--public accountability, international institutions with teeth--are the same ones we needed for what happened (and is still happening), at a fraction of the scale of Xinjiang, in Guantanamo.
"Whataboutism" only works because the whatabouters assume their opponents will reflexively defend the US (or whomever). The implication is, strangely, not "The US has done this too, so we need strong institutions to hold the powerful to account" but, rather, "The US has done this too, so whatareyougonnado?"
Likewise, if someone suspects someone of bias, I don't think it's unimportant to ask them if they hold consistent positions. If a Trump supporter is talking about how Biden should be impeached for something Trump did, I don't think it's "whatboutism" to ask if they would hold the same standard to Trump (or vice versa). There's a big difference between being concerned about something because of an underlying moral principal, and being concerned about something because of a specific bias against one of the groups involved. This used to be considered an important distinction, but now people act as if we shouldn't even talk about it.
[1] https://en.wikipedia.org/wiki/American_Service-Members%27_Pr...