A few months ago, I lost the sound from the HDMI output of my Pi, after an update. I am using the 4gb Pi4. After much cursing and gnashing of teeth, I rebooted, held down the shift key, and reloaded the noobs version of Raspian. The sound worked fine through numerous restarts, that is until I did the update again. Through the months I have tried every thing that I could think of to correct the problem, to no avail. Then I decided to try installing the latest version from the web. I loaded it onto a different micro sd card. Now the sound works just fine after updates. I was looking for the 64 bit beta version, but could not find it, so I loaded the 32 bit full version. All is well with the world once again.
Happy Trails,
Paul
Happy Trails,
Paul