This is an unofficial Forge port of "FabricSkyboxes" by AMereBagatelle. While Forge supports custom skyboxes through Optifine, alternatives like Sodium are becoming more viable, sparking a need for a standalone skybox mod on Forge. This has been tested in a pack with 310+ mods and works fine, but if you run into any issues, please fill out a bug report.
This doesn't support Optifine skypacks directly, but you can convert them using a tool called MCPPPP. If you want a skypack ready to go, we've made a high quality one with 4K textures for our modpacks which you can download here. There are also some posted in #converted-skypacks in AMereBagatelle's Discord (don't bug them about support for this port).
Some screenshots:
