When I use this ShaderGraph and set the GameObject scale.x to -1, the light starts displaying upside down. I duplicated the normal map shader and set the "Two Sided" property to true so that the flipped GameObject could be seen and also added a Flipbook node with the height set to -1 and although the sprites are being affected by the light in the right direction, they aren't displaying properly. Fixing this or giving me a way to do this would mean a lot to my team because our artist has already drawn all the normal maps one by one and the appearance of the game depends on it.

I opened a question in Unity Answers if anyone is interested: https://answers.unity.com/questions/1529041/sprite-normal-map-shadergraph.html