Apparently, i am Canklecat with a slightly healthier neck ( I make up for it with bad shoulders.)

I usually keep my hair in a tight knot on the top of my neck--it is outside the helmet (if ii need to wear one for a gruop ride) and hold the bandana in place nicely otherwise. The knot (Not a "manbun;" I don't even know what they are, but they sound nasty) is small enough (about half a fist) to fit inside most knitted headgear---at least, I have never had a problem. I'd imagine with a skullcap, if you gathered and rubber-banded your hair below the bottom of the skullcap you could fit the skullcap and let the ponytail hang.

You could use the Japanese alternative---samurai used to make a flat ponytail and pull it up over the top of the head and fan it out. might fit in a skullcap that way.

I'd just get a slightly larger skullcap, perhaps ... or cut a hole (and stitch the edges so it doesn't unravel.)