I am also experiencing issues with the orthographic camera in UE 5.3. You can see in the following screenshots that there are issues with the lighting and shadowing when using an orthographic camera:
vs. the perspective camera:
I am running UE on an M1 macbook. Just for reference, both cameras are placed at approximately (-8000, 0, 4500) in world space. The perspective camera has a FOV of 15 degrees, and the ortho camera has a width of ~2300. I have tried removing the exponential height fog but that does not have any effect on my scene. I have also tried multiple settings for global illumination on the ortho camera but they seem to have no effect.