Question Baked shadows on transparent plane in AR view

This may be a long post ,

I wanted to have shadows for the objects that I place on top of the detected planes in the AR view. There are three objects that has been spawned at runtime. Each object have its own primitive plane for receiving shadows from their objects. Each plane have a shader which makes the plane transparent and the shadow visible at Realtime lighting.

Now, the issue is, using Realtime lights for getting shadow, reduces the app's fps after deploying it to mobile device. So I baked the lightmaps but the shadows are not visible on the transparent plane. I feel like something has to be tweaked in the shader. Posting the code here,

Code (CSharp):

1.  
2. Shader "Custom/Shadow"
3. {
4.     Properties  
5.     {
6.         _Color("Main Color", Color) = (1,1,1,1)
7.         _MainTex("Base (RGB)", 2D) = "white" {}  
8.         _Cutoff("Cutout", Range(0,1)) = 0.5 }
9.  
10.         SubShader
11.         {
12.             Pass
13.             {
14.                 Alphatest Greater[_Cutoff]
15.                 SetTexture[_MainTex]
16.             }  
17.            
18.             Pass
19.             {
20.                 Blend DstColor Zero Tags{ "LightMode" = "ForwardBase"
21.             }
22.        
23.         CGPROGRAM
24.  
25.         #pragma vertex vert
26.         #pragma fragment frag
27.         #include "UnityCG.cginc"
28.         #pragma multi_compile_fwdbase
29.         #include "AutoLight.cginc"
30.  
31.         struct v2f
32.         {
33.             float4 pos : SV_POSITION; LIGHTING_COORDS(0,1)
34.         };
35.  
36.         v2f vert(appdata_base v)
37.         {
38.             v2f o; o.pos = UnityObjectToClipPos(v.vertex); TRANSFER_VERTEX_TO_FRAGMENT(o);
39.             return o;
40.         }
41.  
42.         fixed4 frag(v2f i) : COLOR
43.         {
44.             float attenuation = LIGHT_ATTENUATION(i);
45.             return attenuation;
46.         }
47.  
48.         ENDCG
49.      }
50.        
51.    }
52.         Fallback "Transparent/Cutout/VertexLit"
53. }
54.  

How do I make this shader work in baked lights? Any help would be appreciated. I am not using URP because of various reasons and I don't want to use URP for now, as the project is client specific and shortage of time to rectify things if something happens after porting the project to URP. To save the baked lightmaps within the prefab, I use the following

https://github.com/Ayfel/PrefabLightmapping

Versions used:
Unity 2019.4.4f1
AR Foundation preview 3 version 4.0.0
AR Core preview 3 version 4.0.0
AR Subsystems preview 3 version 4.0.0