The project in the video is a completely new HDPR project

1) Create a custom post processing volume script

2) Assign it in the HDRP settings

3) Delete the post processing volume asset

4) Open Graphics settings

Result: On first time viewing Graphic settings, there will be an error in the console. On second time looking at the Graphics settings, the whole Project Settings view would break.

It's quite a painful issue because it kind of bricks your project. After restarting the editor, if you go and try to remove the custom post process from the list, then it will also break the rendering of the Scene view(second video). So if you get into this situation I don't know if there is a way out.

Tested on current trunk