Unfortunately, as of version 4.2, Spine does not have a feature to directly bake physics simulations into keyframes that can be exported to older versions like 3.8. The physics feature is one of the advancements in Spine that relies on the newer runtime support, which is not available in version 3.8. When exporting to an older version, you would lose the physics simulation because it cannot be represented with the keyframes that version 3.8 understands.
However, you can manually keyframe the movements that the physics simulation would produce, essentially creating the animation by hand based on the physics simulation's outcome. This process would be time-consuming and might not capture the dynamic nature of the physics precisely, but it's a workaround to retain the essence of the physics-based animation in a version that does not support the physics feature.
