Migrating your project to Unity’s Universal Render Pipeline can automatically correct materials.

Existing assets imported from the package manager may appear pink:

unity-pink-material

To automatically convert and correct all materials, select Edit » Render Pipeline » Universal Render Pipeline » Upgrade Project Materials to UniversalRP Materials

edit-render-pipeline

Select Proceed in the Material Upgrader dialog window.

material-upgrader

Afterwards, your upgraded scene will appear as it did previously from the basic 3D project.

unity-corrected-materials