alpha cutoff shader from map on map with already existing alpha channel

If for your object with this shader you don't use light, than write shader on HLSL:

  Shader "Custom/CutoutNoLightHLSL" {
   Properties {
    _Color ("Main Color", Color) = (1,1,1,1)
    _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
    _CutTex ("Cutout (A)", 2D) = "white" {}
    _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
   }

   SubShader {
    Tags { "Queue" = "Transparent" }
    Pass {
     ZWrite Off // don't write to depth buffer 
     Blend SrcAlpha OneMinusSrcAlpha // use alpha blending

     CGPROGRAM
 
     #pragma vertex vert
     #pragma fragment frag

     uniform float4 _Color; // define shader property for shaders
     uniform sampler2D _MainTex;
     uniform sampler2D _CutTex;
     uniform float _Cutoff;

     struct vertexInput {
      float4 vertex : POSITION;
      float4 texcoord : TEXCOORD0;
     };
     struct vertexOutput {
      float4 pos : SV_POSITION;
      float4 tex : TEXCOORD0;
     };
 
     vertexOutput vert(vertexInput input) {
      vertexOutput output;
 
      output.tex = input.texcoord;
      output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
      return output;
     }

     float4 frag(vertexOutput input) : COLOR {
      float2 tp = float2(input.tex.x, input.tex.y); //get textures coordinate
      float4 col = tex2D(_MainTex, tp) * _Color; //load main texture
      float newOpacity = tex2D(_CutTex, tp).a; //load cuttext
      if(newOpacity < _Cutoff) {
       newOpacity = 0.0;
      } else { //Calculate new opacity, maybe, other formula. I don't know you parametr of change two textures
       newOpacity = col.a;
       //For example, from your pictures I see, that you change border of two textures as result. Maybe you need next calculation:
       //if (newOpacity < _Cutoff + 0.1) {
       //newOpacity = ((newOpacity - _Cutoff)/(_Cutoff + 0.1 - newOpacity)) * col.a;
       //} else {
       //newOpacity = col.a;
       //}
      }
      return float4(col.r, col.g, col.b, newOpacity);
     }
     ENDCG
    }
   }
  }

But, if you need object with light, write me. Than you need surface shader.I hope that it will help you.