I also had trouble with this. I found it helps to play notes in different octaves, as this often gives away the square sound, which has a bit more bass to it in the low registers, and a flute-like sound in the higher registers, especially the pure square. This especially gets harder once you start to add in filters etc…. I still get it wrong a lot. Keep practicing though, it does get easier.
I am struggling a ton with this myself which is why I came on here.
I like the tip of playing the keys in different octaves.
Do you recommend just doing the same challenges over and over again until they become easier??