There are a lot of conflicting responses as to whether or not Bluetooth 5 is the reason the S8 works with dual audio - as far as I know it is not part of the Bluetooth 5 spec in any way, so Samsung is probably doing something else. Whether or not BT 5 is required to have enough bandwidth to do multiple devices, I don't know.
It doesn't require the devices you connect to it be Bluetooth 5 to work, all A2DP headsets work with dual audio on the Galaxy