Question Shadow Acne Not Influenced At All By Shadow Bias

I'm writing a cel shader and the shadow acne issue occurred.

The problem is that both the normal and depth bias make no difference at all on the shadow, while they do reduced the acne on other objects.
I once copied & pasted someone else's cel shader into the project for testing purposes and the acne appears as well. So probably it is a project/pipeline setting issue instead of a shader issue, but I'm not sure.
I'm using urp and Unity 2020.3.23. Code attached below.

Code (CSharp):

1. Shader "CustomShaders/CelShader"
2. {
3.     Properties
4.     {
5.         _SurfaceColor ("Surface Color", Color) = (1, 1, 1, 1)
6.         _Smoothness ("Smoothness Coefficient", Range(0.0, 1.0)) = 1.0
7.         _RimCoe ("Rim Coefficient", Range(0.0, 1.0)) = 1.0
8.  
9.         _DiffuseThreshold ("Diffuse Threshold",  Range(0.0, 1.0)) = 0.5
10.         _SpecularThreshold ("Specular Threshold",  Range(0.0, 1.0)) = 0.5
11.         _RimThreshold ("Rim Threshold",  Range(0.0, 1.0)) = 0.5
12.         _ShadowThreshold ("Shadow Threshold",  Range(0.0, 1.0)) = 0.5
13.  
14.         //_OutlineScaler ("Outline Scaler",  Range(0.0, 1.0)) = 0.5
15.         //_OutlineColor ("Outline Color", Color) = (0, 0, 0, 1)
16.     }
17.  
18.     HLSLINCLUDE
19.     ENDHLSL
20.  
21.     SubShader
22.     {
23.         Tags { "RenderType"="Opaque" }
24.         LOD 100
25.  
26.         // Cel shader
27.         Pass
28.         {
29.             Cull Back
30.  
31.             Tags
32.             {
33.                 "LightMode" = "UniversalForward"
34.             }
35.  
36.             HLSLPROGRAM
37.             #pragma vertex vert
38.             #pragma fragment frag
39.             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS
40.             #pragma multi_compile _ _MAIN_LIGHT_SHADOWS_CASCADE
41.  
42.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
43.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Lighting.hlsl"
44.             #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Shadows.hlsl"
45.    
46.             struct a2v
47.             {
48.                 float4 vertexOS : POSITION;
49.                 float3 normalOS : NORMAL;
50.                 float2 uv : TEXCOORD0;
51.             };
52.  
53.             struct v2f
54.             {
55.                 float4 vertexCS : SV_POSITION;
56.                 float4 vertexWS : TEXCOORD0;
57.                 float3 normalWS : TEXCOORD1;
58.                 //SHADOW_COORDS(2)
59.             };
60.  
61.             float4 _SurfaceColor;
62.             float _Smoothness;
63.             float _RimCoe;
64.  
65.             float _DiffuseThreshold;
66.             float _SpecularThreshold;
67.             float _RimThreshold;
68.             float _ShadowThreshold;
69.  
70.             v2f vert (a2v v)
71.             {
72.                 v2f o;
73.                 o.vertexCS = mul(UNITY_MATRIX_MVP, v.vertexOS);
74.                 o.vertexWS = mul(UNITY_MATRIX_M, v.vertexOS);
75.                 o.normalWS = mul((float3x3)UNITY_MATRIX_M, v.normalOS);
76.  
77.                 return o;
78.             }
79.  
80.             float4 frag (v2f i) : SV_Target
81.             {
82.                 // Get light
83.                 Light l = GetMainLight(TransformWorldToShadowCoord(i.vertexWS.xyz));
84.  
85.                 // Calculate shadow
86.                 float shadow = step(_ShadowThreshold, saturate(l.shadowAttenuation));
87.  
88.                 // Calculate diffuse
89.                 float diffuse = saturate(dot(i.normalWS, l.direction));
90.                 diffuse *= shadow;
91.                 diffuse = step(_DiffuseThreshold, diffuse);
92.  
93.                 // Get view direction
94.                 float3 viewDirWS = normalize(_WorldSpaceCameraPos.xyz - i.vertexWS.xyz);
95.                 float3 h = normalize(l.direction + viewDirWS);
96.                 // Calculate specular
97.                 float specular = pow(saturate(dot(i.normalWS, h)), exp2(10 * _Smoothness + 1));
98.                 specular *= diffuse * _Smoothness;
99.                 specular = step(_SpecularThreshold, specular);
100.  
101.                 // Calculate rim light
102.                 float rim = 1 - dot(viewDirWS, i.normalWS);
103.                 rim *= pow(diffuse, _RimCoe);
104.                 rim = step(_RimThreshold, rim);
105.  
106.                 // Get ambient
107.                 //float3 ambient = UNITY_LIGHTMODEL_AMBIENT.xyz;
108.                 float3 ambient = float3(unity_SHAr.w, unity_SHAg.w, unity_SHAb.w);
109.  
110.                 float4 outColor = float4(l.color.rgb * (diffuse + max(specular, rim)) + ambient, 1) * _SurfaceColor;
111.  
112.                 return float4(shadow, shadow, shadow, 1);
113.                 //return outColor;
114.             }
115.  
116.             ENDHLSL
117.         }
118.  
119.         // Shadow
120.         UsePass "VertexLit/SHADOWCASTER"
121.     }
122. }
123.