This is a conversions of the old Clouds & Planets skypack, used by SammyGreen and other youtubers. It was initialy created by a LuciSoft / Lucrigo, but was converted to Minecraft by Yuruze. It requires the Fabric Loader and the mod Fabric Skyboxes.
A higher definition version of this skybox (not for minecraft) and others by the creator can be found here. The creator also has a blog where they post other work.