Question Skybox shimmering

I created a skybox with a static cubemap of a city landscape at night but there's a quite annoying effect, the skybox is shimmering andI don't know why.

- Post processing is completely disabled
- The cubemap textures are configured to clamp, with no mipmaps and point filtered
- Alpha source is disabled



I tried various combinations of filters, with and without mipmaps (though it shouldn't have any effect being a skybox) various sizes from 1024 to 4096 and resizing algorithms. The only thing that changes is how blurry the skybox is but the shimmering remains.

Do you have any advice on which setting might be causing the shimmer?
Thanks