Pink is closer to a shader error than a missing texture
When a material becomes bright pink after a URP switch, first check whether its Shader is supported by the active render pipeline. Unity notes that materials must be upgraded when moving from the Built-In Render Pipeline, otherwise they can appear bright pink in Scene view.
That makes the material's Shader and its pipeline support a better first check than reimporting textures or changing colour values.
Inspect project settings and one material together
Confirm whether the project is configured for Built-In, URP, or HDRP, then inspect the Shader on one pink material. For a package or Asset Store asset, check whether the publisher supplies a URP material set or separate import package.
Do not convert an entire production scene as a first experiment. Try a copied sample scene and a few materials, with a version-control commit or project copy available for rollback.
- Check the active Render Pipeline Asset in Project Settings.
- Inspect the Shader name and the asset publisher's pipeline support for one pink material.
- For a Built-In-to-URP move, review applicable options in Window > Rendering > Render Pipeline Converter.
- Convert a small sample scene, then reopen the material and inspect its Shader and texture slots.
A custom shader may need more than the converter
If the Console or Inspector reports a shader error, the problem may be something an automatic converter cannot solve. The practical next step may be a compatible replacement, a Shader Graph recreation, or URP-specific HLSL work.
If only one asset turns pink, avoid changing the project pipeline again until you have checked that asset's support. Verify the material in a target-platform build as well as the Editor.