from kivy.config import Config
Config.set('graphics', 'fullscreen', 0)
#Config.set('graphics', 'resizable', 1)#Может быть понадобится
Config.set('graphics', 'height', 100)
Config.set('graphics', 'width', 100)
Config.write()

In order to avoid situations where the config settings do not work or are not applied before window creation (like setting an initial window size), Config.set should be used before importing any other Kivy modules. Ideally, this means setting them right at the start of your main.py script.