I don't know as I've been doing a lot other things on top of that but for sure crossing your legs will have a negative effect on your circulation, it will tighten up your muscles and mess up your posture which will all negatively affect your nervous system. I do think that I've noticed crossing legs can make my brain fog worse sometimes.
One thing where I do feel instantly a lot better from is stretches for anterior pelvic tilt in the inner quadricep/groin area.