Pico: Why is B15 working against A10 when pwm-ing?

Would be nice to replace those negated PWMs with real PWM channels on the pins that can do both.

Yeah, it would be - unfortunately that's all down to ST who make the chips, not me ;)

I think the negated PWM exists for certain things where you want to use exactly the same PWM but get a normal and inverted output of the same thing at the same time.