We used to play with the house rule that draws stack and transfer until the player is unable to play some kind of deflection. Nothing like sending grandma packing with a Draw 16 stack! (Who am I kidding, granny was the one always whipping our asses at cards! 😭)
It's not a stack. Two players are playing, the +4 also skips the turn of the player it affects. The person who played the +4 is then allowed to play any valid card such as a +4 wild.