Hello,
I am using a RPi4 with the 10.0 Beta (9.95.2) but this problem also occurs with 9.2. There is no audio received by my TV over HDMI but the audio does work over the headphone jack when enabled. I flashed RPi OS and loaded Kodi, then the audio would work. I've searched the forums and tried the "hdmi_drive=2" to no avail. Other methods didn't seem applicable and my knowledge level with Libreelec isn't comfortable enough to dig deeper. Config.txt is the default version with the only change being I've increased the GPU memory to 128MB.
Edit: forgot to mention I'm using the HMDI port next to the USB-C connector.