I just made a clean install of libreelec 9 with Kodi 18 and i no longer have passthrough audio.
The settings are missing and you can not enable the feature.
I have a WeTek Play 1 and it was working fine with version 8.2.5.
My setup is as follows:
* wetek via HDMI ---> TV
* Sony DVD Player used as AMP via optical and HDMI ---> TV
WIth this setup i could hear both the TV and the WeTek out of the surround speakers of the Sony DVD Player
No changes made to the settings of the TV and also no changes in the cabling.
If i can't resolve this issue i guess i will have to downgrade. Any help will be appreciated