All or nothing is something I recognise, relate to. Both the "black-and-white thinking" which is considered more a personality thing, though science and reason helps me to counteract that, and the dissociation between "perfect" mania and "useless"/"inferior" depression. I also feel a vacuum that developed between mania and depression. I have to fill it. I've luckily become better at it, instead of broadening/growing the vacuum.

It is an essential aspect of the more personality/deliberate part of BP, I think. The seeming inability to change it much may create strong emotional reactions: you "should" not do this, there is no apparent reason for it.

I hope you find a way to walk that middle ground.