Example geometry shader running in Unity on Quest.

quest_geometry_shaders_in_multiview.glsl

Shader "Unlit/QuestGEO"
{
	Properties
	{
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }

		Pass
		{
			GLSLPROGRAM
			#version 320 es
			
			// See discussion here https://discussions.unity.com/t/geometry-shaders-in-opengl-multiview/911294
			// It's not "perfect"

#ifdef STEREO_INSTANCING_ON
	// Not used.
    #extension GL_NV_viewport_array2 : enable
    #extension GL_AMD_vertex_shader_layer : enable
    #extension GL_ARB_fragment_layer_viewport : enable
#endif

// ON QUEST, STEREO_MULTIVIEW_ON is enabled.

#ifdef STEREO_MULTIVIEW_ON
	#extension GL_EXT_multiview_tessellation_geometry_shader : enable
	#extension GL_OVR_multiview2 : enable
#endif

			#include "UnityCG.glslinc"
			#include "UnityStereoSupport.glslinc"
			
			#pragma vertex vert
			#pragma fragment frag
			#pragma geometry geo

#ifdef VERTEX

in  vec2 in_TEXCOORD0;
in  vec4 in_POSITION0;


out VS_OUT {
    vec2 ouv;
	float eye;
} vs_out;

uniform  OVR_multiview
{
	uint _ViewID;
	uint numViews_2;
};

layout(std140) uniform UnityStereoEyeIndices {
	vec4 unity_StereoEyeIndices[2];
};

void main ()
{
	vs_out.ouv = in_TEXCOORD0;

	vs_out.eye = 0.0;
	//vs_out.eye = float(gl_ViewID);
	//vs_out.eye = float(_ViewID); // Always 0.
	//vs_out.eye = float(gl_InstanceID); // Always 0.
	//vs_out.eye = float(unity_StereoEyeIndices[gl_ViewID_OVR].x); // Flashes back and forth, just as gl_ViewID_OVR is random.
	//vs_out.eye = float(gl_ViewID_OVR&uint(1)); // view ID is kinda random.
	//vs_out.eye = float(unity_StereoEyeIndex); // Always 0
	gl_Position  = in_POSITION0;
}
#endif 

#ifdef GEOMETRY


layout(triangles) in;
layout(triangle_strip, max_vertices=6) out;

/*
    out gl_PerVertex {
        vec4 gl_Position;
        float gl_PointSize;
        float gl_ClipDistance[];
    };
*/


in VS_OUT {
    vec2 ouv;
	float eye;
} gs_in[];  

out vec2 ouvf;

layout(num_views = 2) in;

// For now, each invocation outputs a triangle to each eye.

	void main()
	{
		int eyeid = 0;
#if defined(STEREO_MULTIVIEW_ON) || defined(STEREO_INSTANCING_ON)
		for( eyeid = 0; eyeid < 2; eyeid++ )
		//eyeid = int(gs_in[0].eye);  // If testing the input instance ID code, uncomment this, and comment out the above line.
#endif
		{
			#if defined(STEREO_MULTIVIEW_ON) || defined(STEREO_INSTANCING_ON)
				mat4 stereoVP = unity_StereoMatrixVP[eyeid];
			#else
				mat4 stereoVP = unity_MatrixVP;
			#endif
			for(int i=0; i<3; i++)
			{
				gl_Position = stereoVP * unity_ObjectToWorld * gl_in[i].gl_Position;
				vec2 o = vec2( gs_in[i].ouv );

				
				gl_Layer = eyeid;
				
				ouvf = o;
				EmitVertex();
			}
			EndPrimitive();
		}
	}

#endif

#ifdef FRAGMENT 
			in vec2 ouvf;
			layout (location = 0) out vec4 color;

			void main()
			{
				color = vec4( mod((ouvf *10.0), 1.0), .1, 1.0 );
			}
			
			
			
			
#endif
			ENDGLSL
		}
	}
}