XPS 13 9370, sound problems after 2004 update

Following the Windows 10 2004 update. I now have no sound. I have tried installing the latest Realtek driver from the Dell site but no joy. The troubleshooter does not seem to help although at one stage it switched to the generic Microsoft HD drive and then it all worked, at least until I rebooted and then it went back to the Realtek driver and I am back to square one. Purchased February 2, 2018. The 2 year warranty expired on February 2, 2020.

I have actually made some progress with this in the last hour and discovered what the problem is. I normally use my Dell with an external monitor which has speakers which I use as they are better quality When I performed the 2004 update, I unplugged the monitor and it wasn't until an hour ago that I plugged it in and the sound was there. However when I go to settings (sound output) and I am presented with the choice of the monitor speakers or my laptop speakers and I select my latter, there is no sound whatsoever. Disconnect the monitor and the result is the same.

Obviously the new driver I have installed from Dell is fine. The troubleshooter reports no problems so what has happened to my speakers. Incidentally I have set my screen preference to laptop only. Something is messed up. I'd be grateful if anyone could throw any light on this.