128x128 skins are mainly used for Minecraft bedrock editions(aka Minecraft windows 10 edition and phone editions), it can be used on Minecraft Java as well but only via mods such as more player models mod ( https://www.curseforge.com/minecraft/mc-mods/more-player-models ) and requires other java players to also be using the mod to see it, but to make/upload a 128x128 skin you can do so from here ( http://minecraft.novaskin.me/resourcepacks#default/assets/minecraft/textures/entity/steve.png )
1 Like