Unique skins that do not show armor, such as the "Baby Ghast" from the "Battle & Beasts 2 Skin Pack" and "R2-D2" & "Yoda" from the "Star Wars Classic Skin Pack," do not show the elytra when equipped. From what I can tell, this started since the 1.16 update. Prior to this update, cape or no cape, the elytra would appear with the appropriate visuals on these skins. Now, only when the elytra is unequipped, can myself and others see the cape I am wearing. I, personally, like to play with the "Baby Ghast" skin and have the elytra act as my "body" with a cape equipped. As it is now, other players have a hard time finding me, as all I am is a head. I would like for the elytra to at least be visible when a cape is equipped.