With Android 10, the Dual Audio function has been removed by name in the system settings. This is because the function is still available.
How the alternative is and how you can transfer music via Bluetooth to two connected devices is described in the following instructions.
Playing media files on multiple devices - this is how it works from Android 10 on
The new function from Android 10 on is "Media" and can be used via the status bar when Bluetooth devices are connected.
1. Pull down the status bar from above with two fingers
2. Select the "Media" button
3. All Bluetooth paired devices are now displayed.
4. Check the devices (max. 2) where the music should be played.
The music will then be played via your Samsung Galaxy S20 on the selected devices.
The Dual Audio function is now taken over by the "Media" function in the notification bar and works just as well as it used to with the Dual Audio function.