Memes

You do understand how saying "two things can be true at once" as if you're talking to an actual toddler is incredibly condescending and not a good place from whence to start a conversation, right? Have the basic respect for someone you're talking and assume they also have object permanence.
Stepping into the room like you're the enlightened Buddha whose shit don't stink, because you just figured out that both Biden and Trump can be senile at the same time, only has the effect to make everyone else look at you like the idiot you are for

1. Not figuring it out earlier and
2. Behaving as if you're presenting some novel insight.

Alternatively if you're trying to dunk on someone have the basic respect for the audience and be either effective or original, which "two things can be true at once" is, ironically, neither.

Edit: its also an incredibly reductive way of approaching geopolitics. Reducing critique of US foreign policy to "our guy bad yes, but their guy bad also!!" is in fact what whataboutism is supposed to describe. It's a rhetorical trick drawing a line where the only discussion about world events can be about wether one of the two things the iniator mentions is more true than another. Bring up a third thing or a more in-depth critique of one of the two pre-existing things and you'll get drowned out.
It's a thought-terminating cliché.