The bug
If any pixels in the pack.png supplied with a resource pack are fully transparent, they will be rendered as fully transparent in-game.
The ticket MC-268929 was swiftly closed as a feature request, in stark contrast to all of the tickets marked as related to it (the only thing remotely close is an older WAI ticket). Given that many of the other tickets related to it have either been fixed so far or are triaged, this may imply that having transparent pixels in pack.png in the first place is not intended design, in contrast to other UI elements.
How to reproduce
Download the attached resource pack and place it in the correct directory
Navigate to the resource packs menu
Expected results
All transparent pixels in pack.png would be rendered opaque.
Actual results
They are rendered transparent.
Linked issues
Attachments
Comments


Bedrock allows semi- and fully transparent pack icons. It could have been a parity change.
Thank you for your report!
However, this issue is Working as Intended.
The report you have submitted is working as intended: see MC-268929.
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Can confirm!