Bare bones Unity project with AR Foundation using the Lightweight Render Pipeline (LWRP) version 5.13
A mashup of https://github.com/Unity-Technologies/LWRP-CustomRendererExamples/ and https://github.com/Unity-Technologies/arfoundation-samples/ as a workaround that allows rendering of the camera background with the latest versions of the LWRP.
Only tested with ARKit.