I've done a little search on various platforms trying to understand what the kms (dtoverlay=vc4-kms-v3d) is doing and to my knowledge is has something to do with the graphics. I also read on raspberry pi forum that "KMS and DRM rely almost exclusively on the EDID of the display, so if that is wrong then you will have issues" which may explain why on my test monitor which is using a DVI to HDMI cable, there is no sound output available in kodi 19. Disabling the kms line enables audio while on that monitor.
Meanwhile I' ve grabbed a small HMDI display with onboard sound and viola, now I have sound output and also sound with the hdmi audio extractor between Pi and display.
So my conclusion is that including dtoverlay=vc4-kms-v3d is not working with all kinds of displays. Strange though that this line is included in the default config.txt when doing a fresh install (
http://os.archlinuxarm.org/os/ArchLinux ... est.tar.gz). I also tested in on my kids RPI4 with LXDE desktop and it produced a very distorted GUI. Trying his RPi4 on another display and it was working fine. Running headless RPI4 like I do on my NAS doesn't even require graphics