Indeed, welcome to limits of computer finity. The further you are the less precision there is, the more such issues occur. Solve by widening the gap.
EEVEE is not as precise as one might think, so it’s better to consider modeling for rendering with it in the spirit of WYSIWYG.
I’ve done solar system in real relative scale. Z fighting was not an issue. But shadows was. This was in a recursive raytracer 20 years ago, not relying on polygons but CSGs. Blender accuracy appears to be quite horrific compared to what I remember back then, but meanwhile in other more poly oriented software I’ve never touched those extremes. So I don’t know how Blender compares to Max, Maya, etc. And I don’t know if you have to do comps in Clarisse to do deep scenes.