enable Button from another Screen

I want to enable a Button from another Screen. However my code doesn't allow it. My method of changing a variable should work in normal python, right?, so why doesn't it work in kivy?

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import BooleanProperty
from kivy.uix.screenmanager import Screen, ScreenManager

class Manager(ScreenManager):
    pass

class Screen1(Screen):
    is_enabled = BooleanProperty(False)

class Screen2(Screen):
    def disable(self):
        Screen1.is_enabled = True
        print("is enabled")

kv = Builder.load_string("""
Manager:
    Screen1:
        name: 'screen1'
    Screen2:
        name: 'screen2'

<Screen1>
    BoxLayout:
        Button:
            text: "test"
            disabled: not root.is_enabled
        Button:
            text: "switch screens"
            on_release:
                app.root.current = "screen2"
                               
<Screen2>
    BoxLayout:
        Button:
            text: "switch screens"
            on_release:
                app.root.current = "screen1"
        Button:
            text: "enable other button"
            on_release:
                root.disable()
 """)

source https://stackoverflow.com/questions/71876664/enable-button-from-another-screen