I am just posting this, partly to display my stupidity, but mostly to help people. I could not get audio to work on Kodi on my new Raspberry Pi4. Nothing would work. It turns out I somehow moved the audio volume in Kodi to zero. When this happens a small red icon in the top right is visible.
Your remote control will not work if it has been hooked up to an amp, as mine is.
To fix this you need a Kodi remote or ssh into LibreElec.
1. Kodi remote is available on all iOS/Android stores. Use this to move the volume back up.
2. SSH in ([email protected] and password) and type 'kodi-remote' for a simple text based controller. ++++
I spent days trying to figure out why the audio was off. Sigh.
Hope this helps someone.