Make your shaders Scriptable Render Pipeline Batcher compatible.

This step by step video tutorial will show you how to convert a custom unlit Built-in shader to the Universal Render Pipeline (URP). It includes a Unity project to follow along with that you can get here: https://github.com/NikLever/Unity_URP_Videos

Get the free e-book: Introduction to the Universal Render Pipeline for advanced Unity creators

Additional resources:
Basic Unlit URP Shader documentation: https://on.unity.com/3Ffitlk
Cyan’s shader code tutorials: https://on.unity.com/3kIZWo2
SamplerState documentation: https://on.unity.com/3vJi3AJ
Naming conventions: https://on.unity.com/38ap3xk