I have a grid with instances. I then added an Empty Sphere and want to rotate all of the instances 90° which are within the range of the Empty Sphere. I figured out to rotate all of the instances at once, but can't figure out how to rotate each instance separately at the location of the Sphere.
You can use the Geometry Proximity node. (You will have to parent a single vert to the empty as the node works with geometry only)
Then using Compare: Less Than to get a boolean output to use as the selection for the Rotate Instances node, you can rotate the instances to 90 deg within the threshold you set in te Compare node.
Now I have used the Empty Display Size as driver to control the threshold. But you can do the same with the scale instead. That will just be a little bit of more work to do.