Windows 10 audio playback fails over bluetooth
Quick google search reveals hundreds of posts having exactly same problem - pairing with bluetooth audio device works but there's no audio. Hundreds of posts with incorrect instructions to fix problem. You do NOT need to uninstall random devices, restart service etc. All you need is correct Bluetooth drivers - drivers NOT available on Windows Update.
Your best bet is to grab drivers from manufacturer website. Don't waste your time in HP or Dell or Lenovo sites but go straight to the source - in my case for Dell DW380 it's Broadcom.
Install drivers, reboot, pair bluetooth speaker, new windows pops up asking if audio should be connected and that's it.