How I can create a Popup when I press a Checkbox in kivy?

I want a pop-up to be created when both a and c are selected in the checkbox.
The popup should show the written: "Both A and C are selected, not well".
I don't want use RadioButton because I want you to be able to select both A and B or B and C

Python file

import kivy
from kivymd.app import App
from kivy.uix.widget import Widget
from kivy.properties import ObjectProperty
from kivy.lang import Builder
from kivy.core.window import Window

Builder.load_file('try.kv')

class MyLayout(Widget):
    checks = []
    def checkbox_click(self, instance, value, topping):
        if value == True:
            MyLayout.checks.append(topping)
            print(MyLayout.checks)
            if "a" in MyLayout.checks and "c" in MyLayout.checks:
                print("not well")
        
        else:
            MyLayout.checks.remove(topping)
            print(MyLayout.checks)
            if "a" in MyLayout.checks and "c" in MyLayout.checks:
                print("not well")


class MyApp(App):
    def build(self):
        return MyLayout()


if __name__ == '__main__':
    MyApp().run()

kv file

<MyLayout>

    GridLayout:
        cols:2

        Label:
            text:"a"
        CheckBox:
            on_active: root.checkbox_click(self, self.active, "a")

        Label:
            text:"b"
        CheckBox:
            on_active: root.checkbox_click(self, self.active, "b")

        Label:
            text:"c"
        CheckBox:
            on_active: root.checkbox_click(self, self.active, "c")