acai I'm not sure what you're trying to accomplish, so I don't know how best to advise you. Since you mention Spine/Sprite, I wonder if you want to use normal maps to do normal based lighting or receive real-time shadows, but what do you really want to do? How do you want your skeletons to look?
To render skeletons in Unity projects using the Universal Render Pipeline, it is common to add the URP Shaders UPM package and use the shaders it provides. You can download the UPM package from the download page: https://esotericsoftware.com/spine-unity-download
And is it okay to assign any shader I made to the Material in the Inspector?
If you follow the "Writing your own shaders" section of the documentation, you should be able to use your own shader. It is generally better to duplicate the shaders provided for Spine and modify them as needed.
https://esotericsoftware.com/spine-unity#Writing-your-own-shaders