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Document Library Custom Hover Card File Preview - Help with JSON
The sample JSON given in question was initially submitted by Tetsuya Kawahara on GitHub. Later he confirmed that this approach is not supported by Microsoft due to security reasons.
Related read: List Formatting - Files can no longer be previewed using filepreview - check comment by Shreyansh Agrawal
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Yes but this feature is not supported now. Rezza also mentioned it as first comment in that YouTube video 
The sample JSON given in question was initially submitted by Tetsuya Kawahara on GitHub. Later he confirmed that this approach is not supported by Microsoft due to security reasons.
Related read: List Formatting - Files can no longer be previewed using filepreview - check comment by Shreyansh Agrawal
Please click Mark as Best Response & Like if my post helped you to solve your issue. This will help others to find the correct solution easily. It also closes the item. If the post was useful in other ways, please consider giving it Like.