Mirillis forum

why can't i turn on both audio tracks when uploading videos to youtube?

YouTube only supports one active audio track per video. If you upload a video with multiple audio tracks, YouTube will typically use the default track. To include multiple audio options, you can:
Merge Tracks: Combine the audio tracks into one using video editing software.
Upload in Multiple Languages: Use YouTube Studio's "Captions" or "Audio" features to add alternate audio tracks for language purposes (if your account supports it).

YouTube only supports one audio track per video. Combine tracks in editing, upload separate versions, or use subtitles for multiple language options.