How to add an alpha mask to this shader ?

I'm running out of ideas and everything I tried so far just causes errors. DAE have an idea of how to add an alpha mask (texture, b/w) to this shader (like a cutout)? I'm starting to lose my mind.

 Shader "Void"
 {
     Properties
     {
         _MainTex ("Base (RGB)", 2D) = "white" {}
     }
     
     SubShader
     {
         Pass
         {
             Tags { "RenderType"="Opaque" }
             LOD 200
         
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
             sampler2D _MainTex;
             float4 _MainTex_ST;
 
             struct v2f
             {
                 float4  pos : SV_POSITION;
                 float4  scrPos;
             };
 
             v2f vert(appdata_base v)
             {
                 v2f o;
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.scrPos = ComputeScreenPos(o.pos);
                 return o;
             }
 
             fixed4 frag(v2f i) : COLOR
             {
                 float2 uv = (i.scrPos.xy / i.scrPos.w);
                 fixed4 c = tex2D(_MainTex, uv);
                 return c;
             }
         
             ENDCG
         } 
     }
         
     FallBack "Diffuse"
 }