There could be several reasons why shadows are not appearing in a Unity project using the Universal Render Pipeline (URP):
Incorrect URP Asset Configuration: The URP asset settings may not be properly configured to allow shadows or may have shadow quality set too low.
Light Settings: The settings for the lights in the scene might not be configured correctly. For example, the light may not be marked to cast shadows, or it might be too far from the objects.
Shader Issues: Custom shaders that do not support shadow casting can cause objects to not cast or receive shadows.
Renderer Feature not Added: In URP, certain features like shadows need to be added explicitly to the renderer's feature list.
Quality Settings Misconfiguration: The Quality settings might be set in a way that prevents shadows from being rendered.
Shadow Distance Too Low: If the shadow distance in the URP settings is too low, shadows might not appear because they're culled at a short distance from the camera.
Incorrect Layer Settings: If the objects are on layers that are not included in the light's shadow-casting settings, shadows won't appear.
Solution - Here's How To Resolve It
Here are potential solutions to resolve issues with shadows not appearing in Unity with URP:
Check the URP Asset: Ensure that the URP asset assigned to the Graphics settings is correctly configured for shadows. Adjust the shadow resolution and other related settings as necessary.
Adjust Light Settings: Verify that your light source is set to cast shadows by selecting the light and enabling shadows in the Inspector panel. Also, make sure it’s close enough and oriented properly relative to objects.
Use URP-Compatible Shaders: Replace any custom shaders with URP-compatible ones, or modify them to support URP's framework for shadow casting and receiving.
Add Renderer Features: Go to your URP asset, select 'Renderer', and ensure that the necessary renderer features, such as screen space shadows, are added.
Configure Quality Settings: Navigate to Edit > Project Settings > Quality and ensure that the shadow settings are enabled and properly configured.
Increase Shadow Distance: In the URP settings, increase the shadow distance so it covers the area where you expect shadows to appear.
Layer Settings: Make sure the object layers are included in the shadow-casting settings of your lights. Check both the layer of the object and the Culling Mask setting on the light.
By systematically checking each of these potential issues, you should be able to diagnose and fix the problem causing shadows not to work in your Unity URP project.