How can I solve the problem of using URP to darken Sprite without light
Among the material presets for URP provided by AnyPortrait, try using the preset labeled “Unlit.”
All materials named "~ Unlit" are unaffected by lights.
You can see the results of applying Unlit and Lit materials in the following manual.
Note that, "Built-in" materials other than URP are affected by "Ambient light" even if they are "Unlit".
If you have any more questions, please leave a comment!