Duckduckgo.com is Raspberry friendly
and is a search engine that
actually gives the correct
technical information about
how to install things on
Raspberry.

Most other OS'es for Raspberry while
cool don't work on all Raspberries
and some don't offer solutions on
more than some points.

To get HDMI sound and to get Bluetooth
sound on Raspberry PI OS with standard
Raspberry PI 3 I followed the first part
of this:

https://youness.net/raspberry-pi/how-to-connect-bluetooth-headset-or-speaker-to-raspberry-pi-3

I then installed
sudo apt install pavucontrol

and started it

pavucontrol &

And I followed the terminal commands in this, 
and it started working as I changed
device=1 to device=2 in the line
that tests audio

https://wiretuts.com/connecting-bluetooth-audio-device-to-raspberry-pi

Suddenly all worked :)