Lighting Mode property is just an Editor GUI parameter which switches between shaders. You can check out the code in SpineSpriteShaderGUI.cs, line 368.
Why would want to change
Lighting Mode at runtime when using URP? When using URP with a 2D Renderer, the only valid Sprite shader is
"Universal Render Pipeline/2D/Spine/Sprite" and when using URP with a normal (non-2D) Renderer,
"Universal Render Pipeline/Spine/Sprite" is the only valid one.