import bpy
from bpy.types import Panel, Operator, PropertyGroup
from bpy.props import EnumProperty, PointerProperty


class MyProperties(PropertyGroup):

    my_enum : EnumProperty(
        name= "Enumerator / Dropdown",
        description= "sample text",
        items= [('OP1', "Add Cube", ""),
                ('OP2', "Add Sphere", ""),
                ('OP3', "Add Suzanne", "")
        ]
    )

class ADDONNAME_PT_main_panel(Panel):
    bl_label = "Main Panel"
    bl_idname = "ADDONNAME_PT_main_panel"
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'UI'
    bl_category = "New Tab"

    def draw(self, context):
        layout = self.layout
        scene = context.scene
        mytool = scene.my_tool


        layout.prop(mytool, "my_enum")
        layout.operator("addonname.myop_operator")





class ADDONNAME_OT_my_op(Operator):
    bl_label = "Add Object"
    bl_idname = "addonname.myop_operator"

    def execute(self, context):
        scene = context.scene
        mytool = scene.my_tool

        return {'FINISHED'}




classes = [MyProperties, ADDONNAME_PT_main_panel, ADDONNAME_OT_my_op]


def register():
    for cls in classes:
        bpy.utils.register_class(cls)

    bpy.types.Scene.my_tool = PointerProperty(type= MyProperties)

def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)
    del bpy.types.Scene.my_tool



if __name__ == "__main__":
    register()