My attempt to make a splatmap with Albedo, Metallic, Roughness, Normal and AO.

Godot Splatmap Shader T02

shader_type spatial;

render_mode blend_mix,depth_draw_opaque,cull_disabled,diffuse_burley,specular_schlick_ggx;

uniform sampler2D splatmap;

uniform sampler2D groundBaseColor: hint_albedo;
uniform float groundSpecular = 0.5;
uniform float groundMetallic;
uniform float groundRoughness : hint_range(0,1);
uniform float groundPoint_size : hint_range(0,128) = 1;
uniform sampler2D groundMetallicTexture : hint_white;
uniform vec4 groundMetallicTexture_channel = vec4(1, 0, 0, 0);
uniform sampler2D groundRoughnessTexture : hint_white;
uniform vec4 groundRoughnessTexture_channel = vec4(0, 1, 0, 0);
uniform sampler2D groundNormalTexture : hint_normal;
uniform float groundNormalTexture_scale : hint_range(-16,16) = 1;
uniform float groundTexturesRes = 1;
uniform sampler2D groundAmbientOcclusionTexture : hint_white;
uniform vec4 groundAmbientOcclusionTexture_channel = vec4(0, 0, 1, 0);
uniform float groundA_O_Texture_light_affect = 1;

uniform sampler2D dirtBaseColor: hint_albedo;
uniform float dirtSpecular = 0.5;
uniform float dirtMetallic;
uniform float dirtRoughness : hint_range(0,1);
uniform float dirtPoint_size : hint_range(0,128) = 1;
uniform sampler2D dirtMetallicTexture : hint_white;
uniform vec4 dirtMetallicTexture_channel = vec4(1, 0, 0, 0);
uniform sampler2D dirtRoughnessTexture : hint_white;
uniform vec4 dirtRoughnessTexture_channel = vec4(0, 1, 0, 0);
uniform sampler2D dirtNormalTexture : hint_normal;
uniform float dirtNormalTexture_scale : hint_range(-16,16) = 1;
uniform float dirtTexturesRes = 1;
uniform sampler2D dirtAmbientOcclusionTexture : hint_white;
uniform vec4 dirtAmbientOcclusionTexture_channel = vec4(0, 0, 1, 0);
uniform float dirtA_O_Texture_light_affect = 1;

uniform sampler2D cliffBaseColor: hint_albedo;
uniform float cliffSpecular = 0.5;
uniform float cliffMetallic;
uniform float cliffRoughness : hint_range(0,1);
uniform float cliffPoint_size : hint_range(0,128) = 1;
uniform sampler2D cliffMetallicTexture : hint_white;
uniform vec4 cliffMetallicTexture_channel = vec4(1, 0, 0, 0);
uniform sampler2D cliffRoughnessTexture : hint_white;
uniform vec4 cliffRoughnessTexture_channel = vec4(0, 1, 0, 0);
uniform sampler2D cliffNormalTexture : hint_normal;
uniform float cliffNormalTexture_scale : hint_range(-16,16) = 1;
uniform float cliffTexturesRes = 1;
uniform sampler2D cliffAmbientOcclusionTexture : hint_white;
uniform vec4 cliffAmbientOcclusionTexture_channel = vec4(0, 0, 1, 0);
uniform float cliffA_O_Texture_light_affect = 1;

uniform sampler2D snowBaseColor: hint_albedo;
uniform float snowSpecular = 0.5;
uniform float snowMetallic;
uniform float snowRoughness : hint_range(0,1);
uniform float snowPoint_size : hint_range(0,128) = 1;
uniform sampler2D snowMetallicTexture : hint_white;
uniform vec4 snowMetallicTexture_channel = vec4(1, 0, 0, 0);
uniform sampler2D snowRoughnessTexture : hint_white;
uniform vec4 snowRoughnessTexture_channel = vec4(0, 1, 0, 0);
uniform sampler2D snowNormalTexture : hint_normal;
uniform float snowNormalTexture_scale : hint_range(-16,16) = 1;
uniform float snowTexturesRes = 1;
uniform sampler2D snowAmbientOcclusionTexture : hint_white;
uniform vec4 snowAmbientOcclusionTexture_channel = vec4(0, 0, 1, 0);
uniform float snowA_O_Texture_light_affect = 1;

uniform vec3 uv1_scale = vec3(1);
uniform vec3 uv1_offset;

void vertex() {
	UV=UV*uv1_scale.xy+uv1_offset.xy;
}

void fragment() {
	vec3 splatmapColor;
	
	vec3 groundColor;
	vec3 dirtColor;
	vec3 cliffColor;
	vec3 snowColor;
	
	splatmapColor = texture(splatmap, UV).rgb;
	
	groundColor = texture(groundBaseColor, UV * groundTexturesRes).rgb;
	dirtColor = texture(dirtBaseColor, UV * dirtTexturesRes).rgb * splatmapColor.r;
	cliffColor = texture(cliffBaseColor, UV * cliffTexturesRes).rgb * splatmapColor.b;
	snowColor = texture(snowBaseColor, UV * snowTexturesRes).rgb * splatmapColor.g;

	ALBEDO = groundColor + dirtColor + cliffColor + snowColor;
	
	
	float ground_metallic_tex = dot(texture(groundMetallicTexture, UV), groundMetallicTexture_channel);
	float dirt_metallic_tex = dot(texture(dirtMetallicTexture, UV), dirtMetallicTexture_channel) * splatmapColor.r;
	float cliff_metallic_tex = dot(texture(cliffMetallicTexture, UV), cliffMetallicTexture_channel) * splatmapColor.b;
	float snow_metallic_tex = dot(texture(snowMetallicTexture, UV), snowMetallicTexture_channel) * splatmapColor.g;
	
	float ground_metallic = ground_metallic_tex * groundMetallic;
	float dirt_metallic = dirt_metallic_tex * dirtMetallic;
	float cliff_metallic = cliff_metallic_tex * cliffMetallic;
	float snow_metallic = snow_metallic_tex * snowMetallic;
	
	METALLIC = ground_metallic + dirt_metallic + cliff_metallic + snow_metallic;
	
	
	float ground_roughness_tex = dot(texture(groundRoughnessTexture, UV * groundTexturesRes), groundRoughnessTexture_channel);
	float dirt_roughness_tex = dot(texture(dirtRoughnessTexture, UV * groundTexturesRes), dirtRoughnessTexture_channel) * splatmapColor.r;
	float cliff_roughness_tex = dot(texture(cliffRoughnessTexture, UV * groundTexturesRes), cliffRoughnessTexture_channel) * splatmapColor.b;
	float snow_roughness_tex = dot(texture(snowRoughnessTexture, UV * groundTexturesRes), snowRoughnessTexture_channel) * splatmapColor.g;
	
	float ground_roughness = ground_roughness_tex * groundRoughness;
	float dirt_roughness = dirt_roughness_tex * dirtRoughness;
	float cliff_roughness = cliff_roughness_tex * cliffRoughness;
	float snow_roughness = snow_roughness_tex * snowRoughness;
	
	ROUGHNESS = ground_roughness + dirt_roughness + cliff_roughness + snow_roughness;
	
	
	SPECULAR = groundSpecular + (dirtSpecular * splatmapColor.r) + (cliffSpecular * splatmapColor.b) + (snowSpecular * splatmapColor.g);
	
	
	vec3 groundNormal = texture(groundNormalTexture, UV * groundTexturesRes).rgb;
	vec3 dirtNormal = texture(dirtNormalTexture, UV * dirtTexturesRes).rgb * splatmapColor.r;
	vec3 cliffNormal = texture(cliffNormalTexture, UV * cliffTexturesRes).rgb * splatmapColor.b;
	vec3 snowNormal = texture(snowNormalTexture, UV * snowTexturesRes).rgb * splatmapColor.g;
	
	NORMALMAP = groundNormal + dirtNormal + cliffNormal + snowNormal;
	NORMALMAP_DEPTH = groundNormalTexture_scale + dirtNormalTexture_scale + cliffNormalTexture_scale + snowNormalTexture_scale;
	
	
	float ground_AO = dot(texture(groundAmbientOcclusionTexture, UV * dirtTexturesRes), groundAmbientOcclusionTexture_channel);
	float dirt_AO = dot(texture(dirtAmbientOcclusionTexture, UV * dirtTexturesRes), dirtAmbientOcclusionTexture_channel) * splatmapColor.r;
	float cliff_AO = dot(texture(cliffAmbientOcclusionTexture, UV * cliffTexturesRes), cliffAmbientOcclusionTexture_channel) * splatmapColor.b;
	float snow_AO = dot(texture(snowAmbientOcclusionTexture, UV * snowTexturesRes), snowAmbientOcclusionTexture_channel) * splatmapColor.g;
	
	AO = ground_AO + dirt_AO + cliff_AO + snow_AO;
	AO_LIGHT_AFFECT = groundA_O_Texture_light_affect + (dirtA_O_Texture_light_affect * splatmapColor.r) + (cliffA_O_Texture_light_affect * splatmapColor.b) + (snowA_O_Texture_light_affect * splatmapColor.g);
	
}