Relevant part
The FIA has issued a directive to control the costs related to other sport equipments of the teams, such as boat designs, bikes or road vehicles, in order to avoid that the personnel employed in such areas is used to make further research useful for the F1 team avoiding the budget cap. Request of clarification issued to Mercedes, Ferrari, Red Bull and Aston Martin.
“No FIA this Aero Engineer is needed to improve our cans!” - Red Bull, probably
Red Bull literally had the Red Bull Air Racing Championship until 2019. Now I wonder if that was a secret F1 research endeavor.
There was no budget cap, there were no need to hide it
Red Bull gives you front wings