unity – Why is _GrabTexture(texture of present body buffer) at all times empty in my code and the way do I repair it?

Here’s a fragment shader I wrote that makes use of a seize move to copy an “common coloration” mix mode

Shader "2DSB/VertexColor" 
{
    Properties
    {
        [PerRendererData] _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
        _Color ("Principal Coloration", Coloration) = (1, 1, 1, 1)
    }

    SubShader
    {
        Tags {"Queue"="Clear" "IgnoreProjector"="True" "RenderType"="Clear"}
        ZWrite Off
        Lighting Off
        Cull Off
        Fog { Mode Off }
        //Earlier: Mix SrcAlpha OneMinusSrcAlpha
        Mix SrcAlpha Zero
        LOD 100

        // Add GrabPass to seize the present body buffer
        GrabPass { } // "_GrabTexture" is the title of the grabbed texture
        
        Cross
        {
            CGPROGRAM
            #pragma vertex vert_vct
            #pragma fragment frag_mult
            #pragma fragmentoption ARB_precision_hint_fastest
            #embrace "UnityCG.cginc"

            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _GrabTexture;
            float4 _GrabTexture_ST;
            float4 _Color;

            struct vin_vct
            {
                float4 vertex : POSITION;
                float4 coloration : COLOR;
                float2 texcoord : TEXCOORD0;
            };

            struct v2f_vct
            {
                float4 vertex : SV_POSITION;
                fixed4 coloration : COLOR;
                float2 texcoord : TEXCOORD0;
                float2 screenspaceUV : TEXCOORD1; // Add display screen area UV
            };

            v2f_vct vert_vct(vin_vct v)
            {
                v2f_vct o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.coloration = v.coloration;
                o.texcoord = v.texcoord;
                o.screenspaceUV = ComputeScreenPos(o.vertex).xy; // Compute display screen area place
                return o;
            }

            fixed4 frag_mult(v2f_vct i) : SV_Target
            {
                fixed4 srcColor = tex2D(_MainTex, i.texcoord) * i.coloration * _Color;
                fixed4 dstColor = tex2D(_GrabTexture, i.screenspaceUV); // Coloration from the body buffer; Use display screen area UV to pattern
                
                // Customized logic to common the colours
                fixed4 finalColor = srcColor;
                if (any(dstColor.rgba > fixed4(0,0,0,0).rgba)) { // Why is that this by no means true, even when there's overlap between sport objects?
                    finalColor = (srcColor + dstColor) * 0.5; // Easy averaging
                    //Take a look at: finalColor = fixed4(1,0,0,1);
                }

                return finalColor;
            }
            
            ENDCG
        } 
    }
}

The large drawback is that the sampled _GrabTexture is at all times empty. I do know this as a result of this block was by no means true.

if (any(dstColor.rgba > fixed4(0,0,0,0).rgba)) { // Why is that this by no means true, even when there's overlap between sport objects?
                    finalColor = (srcColor + dstColor) * 0.5; // Easy averaging
                    //Take a look at: finalColor = fixed4(1,0,0,1);
                }

Nonetheless, this needs to be true for areas the place there are overlapping sport objects. What’s the challenge right here? How do I appropriately pattern the present body buffer’s texture utilizing GrabPass to implement a median colours mix mode?