Using a Texture Cube on a Skybox

Hey guys!
I just used Spacescape to make a custom Skybox and imported it to Unreal 5.
I followed a couple tutorials on how to use the file for a custom Skybox. It all went well but when I’m using the material, my Skybox has this sharp edges inside and I don’t kow how to fix it.

Is there a problem on how I imported the file? It’s a .dds file with the highest resolution. I changed its texture group to Skybox and No Mipmaps.
Even the Texture Cube itself looks like this when I open it…


Unbenannt

So yeah, maybe someone can help me with this issue. Thanks in advance:)