GL immediate mode geometry generated via script in OnPostRender does not appear in Game view during Play mode when the Scriptable Render Pipeline Settings from the Lightweight Render Pipeline for VR template are used.

Changing the Scriptable Render Pipeline Settings to None in Graphics settings enables the immediate mode geometry to appear.

The behaviour is the same whether VR is disabled in Player settings, or whether VR is enabled and Mock HMD is the only entry in the VR SDK list.