I spent last 3 days looking through the net to find an answer for that... In short - my bluetooth device was connecting to PC, it was visible under Bluetooth devices as connected, with the green dot and all that, but it wasn't listed as an Audio Output device, and it was not possible to "Enable" it in the oldschool audio "playback and input" menu. I have bought new soundbar, because i thought something broke with my previous BT speakers (although those were working absolutely fine with both Android and Apple devices)... Nevertheless, try this:
Go to Settings -> Bluetooth and devices -> (all the way down) More devices and printer setting
Your BT audio output device (soundbar, headphones etc) should be listed there. Right click on it -> Properties -> Hardware tab
In there click on the line which contain "AVRCP" mentioned somewhere within (might need to enlarge column to see it) -> click Properties
In the "general tab" of this new window click -> Change settings
Go to "Driver tab" and choose -> update Driver, then -> Browse my computer for drivers -> Let me pick from a list of available drivers -> AND THEN, choose this exact one -> "Microsoft Bluetooth AVRCP Transport Driver.
Reconnect the device if needed.
It takes around 2 minutes to do all this, hopefully this helps!
Worked for me.
This finally solved it. Thank you!