If the Earth was feeling a gravitational force corresponding to the relative position where the sun appeared to be 8.5 minutes ago, instead of where it currentl

If the Earth was feeling a gravitational force corresponding to the relative position where the sun appeared to be 8.5 minutes ago, instead of where it currently is, then it would lose orbital angular momentum I can’t understand why. If we imagine a completely dark universe of pointlike massive bodies, orbits still should work. Light and gravity not in sync should not change gravity? If that was obvious, why LIGO(iirc?) wanted to detect gravitational waves?