Why doesn't Himawari have a Jougan?
It is not a plot hole or something other than it. It is based on that she is still a child and has to mature in order to learn the techniques and the hidden agendas. Maybe in the future we might see her as a sage with powers comparing to that of Naruto and might even unlock the hidden potential inside of her because her grandpa is a byakugan user and he very much loves his grandchildren. So, we might be in for a treat to witness her greatness and she might spar with her brother in the future since you know, they are siblings with overwhelming powers