Hello ,
Thank you for posting in the community your question and for your patience while I looked into the videos and tutorial you were referencing. I believe you were looking at Video 3 and 4 on this playlist: https://youtube.com/playlist?list=PL-qDTLDChBlkIGUxPB2WCtubMXeIOV0TM
The VR Animation player works with JPEG but not PNG with the most current update: https://www.oculus.com/experiences/quest/2515021945210953/
In his video he is using an older version of the VR Animation player which could be why the PNG might have worked. You might be able to contact VR Animation player for further support as this is specific to their software and might be able to provide further input why PNG format is nor working on that app. I was able to reproduce the same behavior on my end as well.
Please use JPEG format with VR Animation Player to avoid those black screen issues.
Kind regards,
Vincent B.