Some people might wonder what the big deal is. It’s just a funny face (Cyrus, for one denied that it was mocking Asians at all).
All I know is, I grew up with (white) kids making the same face to me: leering, making buck-teeth smiles, pulling their eyes back and saying “Ah-so!” and laughing crazily like they’d just done something really clever.
It wasn’t cute or funny then, and it isn’t cute or funny now.
It made me sick to my stomach as a kid who felt disempowered, and seeing famous (white) people doing it now brings all the bile right back up again.