Oh... I solved it. The issue was caused by setting the "Order in Layer" to 1.

If turn off ZWrite

      // ZWrite Off

The character is hidden

The spine character's Z value is less than that of the transparent object, but it is rendered overlaying it.

Why does it behave like this?
How can the character be rendered behind the transparent object?

Here is the transparent obj shader codes

Shader "Custom/TransparentTex"
{
  Properties
  {
    _MainTex("Base Texture", 2D) = "white" {}
    _Color("Color", Color) = (1, 1, 1, 1)
    _TexLod("Texure LOD", Float) = 0.0

    [Enum(UnityEngine.Rendering.BlendMode)]
    _SrcBlend("Source blend Factor", Int) = 1
    [Enum(UnityEngine.Rendering.BlendMode)]
    _DstBlend("Destination blend Factor", Int) = 1
  }
  SubShader
  {
    Tags
    {
      "RenderType" = "Transparent"
      "Queue" = "Transparent"
      "RenderPipeline" = "UniversalPipeline"
    }

    pass
    {
      Blend [_SrcBlend] [_DstBlend]
      ZWrite Off

      HLSLPROGRAM
      #pragma target 3.0
      #pragma vertex vert
      #pragma fragment frag
      #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

      sampler2D _MainTex;
      CBUFFER_START(UnityPerMaterial)
        float4 _Color;
        float4 _MainTex_ST;
        float _TexLod;
      CBUFFER_END

      struct appdata
      {
        float4 positionOS: POSITION;
        float2 uv: TEXCOORD0;
      };

      struct v2f
      {
        float4 positionCS: SV_POSITION;
        float2 uv: TEXCOORD0;
      };

      v2f vert(appdata inputData)
      {
        v2f outData;
        outData.positionCS = TransformObjectToHClip(inputData.positionOS);
        outData.uv = TRANSFORM_TEX(inputData.uv, _MainTex);
        return outData;
      }

      float4 frag(v2f inputData) : SV_TARGET
      {
        float4 sampleUVs = float4(inputData.uv, 0.0f, _TexLod);
        float4 textureSample = tex2Dlod(_MainTex, sampleUVs);
        return textureSample * _Color;
      }

      ENDHLSL
    }
  }
  FallBack "Diffuse"
}

#2372
Here is the Godot4 project file

Godot version: v4.1.1.stable.custom_build.bd6af8e0e

Godot downloaded from spine-godot