Does anyone else remember a Minecraft biome that was in the sky?

Vanilla Minecraft has never had any biomes or islands in the sky, unless a natural generation of a mountain cause a peak to float or the landmass floating in the Nether. There's mods like the Aether which add a paradise dimension with floating islands

Are you confusing it with a mod? There are plenty of mods that add floating islands, the most common one is Tinkers' Construct which adds Slime Islands in the sky.

You could also be remembering a custom map, maybe a server you joined. A lot of servers go for the floating island aesthetic

Yep. Skyworld.
It was removed I think. Didn't work too well.

Yes. I remember on minecraft

It might have been the aether mod. It wasn't official, but it was a whole dimension like the nether with unique blocks and mobs. You made a portal with glowstone and water, similar to the nether portal