Dual Audio Output

Hi! I have an iPhone 11 Pro Max, with iOS 14.6. I am able to connect two bluetooth speakers at the same time, however I do not have an option of playing both of them simultaneously. When I go to AirPlay, I only get to choose one output, not the both (like shown on the photo attached). I have already tried disconnecting and forgetting the bluetooth devices, as well as changing the classifications of them, nothing helps.