Having just found a Unity video about custom Gizmos I decided to give it a try. Found this link: Editor Scripting | UdonSharp
Having a few issues: Note the hyperlink provided does not link to the example. The path has obviously changed.
Meanwhile I found it here: UdonSharp/Packages/com.vrchat.UdonSharp/Samples~/CustomInspectors/CustomInspectorChildBehaviour.cs at master · vrchat-community/UdonSharp · GitHub
It isn’t working for me. And this.UpdateProxy mentioned in the docs is marked as obsolete.
Does this work?