If it's working with any other apps let us know. As it's not working with any other app, it's could be your device limitation.
There are so many Android TV devices & not all of them supports pass through. Until or unless we have proper logs, we can't identify the issue.
The issue reported by @legelek might be different as it works with others. Some HDMI devices do not report the supported decoders. It might be due to failure to identify the decoders supported by the HDMI device. We can confirm it only after looking at the logs.