The camera+spring arm are components of the characters blueprint, controlled by adding yaw and pitch input to the player controller. Camera of the horse is unecessary and could be removed if everything work as intended.
How would you use the camera attached to a third actor and why?
The problem is still the same, the camera will still switch when unpossessing the player character to possess the horse character unless I find why there’s an automatic camera switch while “Auto Manage Active Camera Target” is set to false.