A bit late on reporting on this but it did solve the problem when muxed with MKVtoolnix and I can even switch between 2 audio files now.
Thanks for the detailed explanation and will keep you posted on the results.
I have a 4K mkv video file (Dolby Vision, Version 1.0, dvhe.08.06, BL+RPU, HDR10 compatible / SMPTE ST 2086, HDR10) muxed with HE-AAC 8 channels...
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