Minecraft skins with transparent outer layers don't display to other players. The issue effects 1.14.4 and up. The owner of a Minecraft skin will see the transparent portions of their skin, but any outside players see solid textures. A player viewing someone with transparent outer layers will only see solid outer layers.
The picture below is of a friend on Hypixel, the red outer layer is supposed to be transparent, but doesn't appear so.
Cannot reproduce; tested it in 20w18a and the outer semi-transparent layer displayed correctly for both players.