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How to uncompress a texture?

the best thing I can come up with is using no Mipmap, but it is still compress.

so I thought it is possible to make a checker pattern with 2x2 pixel right?
but the texture is automatically compressed when it is imported in Unreal Engine.

You can set Compression Settings to UserInterface2D.
But question is what you are trying to achieve? Texture compression is huge memory and performance save. Also mipmaps are needed for antialiasing and performance.