At first this might seem like a simple change on purpose but this wasn't mentioned in any changelog and upon looking at the code, I found the issue. This seems to not be on purpose at all, and is infact a bug.

The issue appears to be that in SkyRenderer#renderDarkDisc it is using PoseStack and calling translate, but upon rendering/calling drawWithRenderType, it is not using the PoseStack at all and instead is using the ModelViewStack from RenderSystem which is unaffected by the PoseStack.

The fix to this would be to replace the used poseStack calls in SkyRenderer#renderDarkDisc with ModelViewStack calls from RenderSystem.

Upon testing, that fixes it.

1.21.1

1.21.2+