Jesusemora this does not work.
Code that sets stuff on mouse over:
if collider is Item:
var mesh :MeshInstance3D = collider.item_mesh
var material_count = mesh.get_surface_override_material_count()
if is_mouse_entered:
print(mesh)
mesh.set_instance_shader_parameter("uniform",1.0)
mesh.set_instance_shader_parameter("grow",0.05)
mesh.set_instance_shader_parameter("albedo",Color.CHARTREUSE)
else:
mesh.set_instance_shader_parameter("uniform",0.0)
mesh.set_instance_shader_parameter("grow",0.0)
mesh.set_instance_shader_parameter("albedo",Color.BLACK)

shader code:
// NOTE: Shader automatically converted from Godot Engine 4.2.1.stable's StandardMaterial3D.
shader_type spatial;
render_mode blend_mix,depth_draw_opaque,cull_back,diffuse_burley,specular_schlick_ggx;
uniform vec4 albedo : source_color;
uniform sampler2D texture_albedo : source_color,filter_linear_mipmap,repeat_enable;
uniform float point_size : hint_range(0,128);
uniform float roughness : hint_range(0,1);
uniform sampler2D texture_metallic : hint_default_white,filter_linear_mipmap,repeat_enable;
uniform vec4 metallic_texture_channel;
uniform sampler2D texture_roughness : hint_roughness_r,filter_linear_mipmap,repeat_enable;
uniform float specular;
uniform float metallic;
uniform vec3 uv1_scale;
uniform vec3 uv1_offset;
uniform vec3 uv2_scale;
uniform vec3 uv2_offset;
instance uniform float grow = 0.0;
void vertex() {
UV=UV*uv1_scale.xy+uv1_offset.xy;
}
void fragment() {
vec2 base_uv = UV;
vec4 albedo_tex = texture(texture_albedo,base_uv);
ALBEDO = albedo.rgb * albedo_tex.rgb;
float metallic_tex = dot(texture(texture_metallic,base_uv),metallic_texture_channel);
METALLIC = metallic_tex * metallic;
vec4 roughness_texture_channel = vec4(1.0,0.0,0.0,0.0);
float roughness_tex = dot(texture(texture_roughness,base_uv),roughness_texture_channel);
ROUGHNESS = roughness_tex * roughness;
SPECULAR = specular;
}
