Receive Shadows after vertex transfrmation

Hy, I want to implement a low poli water in my game. At first I was creating a new mesh every frame which was very inperformant. Then i decided to write a vertex shader for that. Now this works and i have moving vertices. The problem is that the mesh now doesn't recieve dynamic shadows. It just shows up the shadow before giong to play mode and doesn't change it. Then I found "Tags {"LightMode" = "ShadowCaster"}". Now a dynamic shadow show up, and the vertices are transforming, but the material of my mesh doesn't change. Am I completly missing something? Here is my shadercode

  Shader "Custom/Water2" {
         Properties {
             _Color ("Color", Color) = (1,1,1,1)
             _MainTex ("Albedo (RGB)", 2D) = "white" {}
             
             _Scale("Scale", float) = 1
             _Speed("Speed", float) = 1
             _Frequency("Frequency", float) = 1
         }
         SubShader {
             //Tags { "RenderType"="Opaque" }
             //Tags {"LightMode" = "ShadowCaster"}
             LOD 200
             
             CGPROGRAM
             // Physically based Standard lighting model, and enable shadows on all light types
             #pragma surface surf Standard fullforwardshadows vertex:vert
     
             // Use shader model 3.0 target, to get nicer looking lighting
             #pragma target 3.0
     
             sampler2D _MainTex;
             float _Scale, _Speed, _Frequency;
             
             struct Input {
                 float2 uv_MainTex;
             };
             fixed4 _Color;
             
             void vert(inout appdata_full v){
                 half offsetvert = (v.vertex.x * v.vertex.x) + (v.vertex.z * v.vertex.z);
                 half value = _Scale * sin(_Time.w * _Speed + offsetvert * _Frequency);
                 
                 v.vertex.y += value;
             }
     
             void surf (Input IN, inout SurfaceOutputStandard o) {
                 o.Albedo = _Color;
             }
             ENDCG
         } 
         FallBack "Diffuse"
     }

The picture below shows the transformed vertex and the static (not transforming )material.

Thanks for your help! [1]: /storage/temp/53446-question-shader.png