The following is a problem I have with the kivy module. When I created my first 3-4 widgets of the FirstScreen class – everything was fine, but after that the widgets started to occupy the same space that they used to, without expanding up. Maybe it’s a problem of the ScrollView. There is no kv file
the widgets are shown here

from functools import partial

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.uix.label import Label
from kivy.uix.popup import Popup
from kivy.uix.screenmanager import Screen, ScreenManager, NoTransition
from kivy.uix.scrollview import ScrollView
from kivy.uix.textinput import TextInput

class YogaApp(App):
    def build(self):
        self.sm = ScreenManager(transition=NoTransition())
        self.sm.add_widget(FirstScreen(name='First'))
        self.sm.add_widget(SecondScreen(name='Second'))
        self.sm.add_widget(ThirdScreen(name='Third'))
        self.sm.add_widget(FourthScreen(name='Fourth'))
        self.sm.add_widget(FifthScreen(name='Fifth'))
        # self.sm.current = 'Second' # Для того чтобы тестировать шаблоны. УБРАТЬ ПОТОМ
        return self.sm
    def change_screen_manager(self, screen):
        self.sm.current = screen

class FirstScreen(Screen):
    """The first screen the user sees. It is the screen for creating a workout or a workout
    template. It also shows all of your created templates which you can click for the second
    screen to pop up
    """
    total_training_sessions = 0
    total_training_sessions_text = 'Всего тренировок: ' + str(total_training_sessions)
    # Это шаблоны тренировок
    templates = {}
    # А это все упражнения
    # exercises = []

    def __init__(self, **kwargs):
        """
        Creates all widgets and adds them on the first screen. Creates templates that
        are a button with the text of the name and the exercises of the template.
        It does so by extracting the template name and values from the dictionary 'templates'
        
        :param kwargs:
        """
        super(FirstScreen, self).__init__(**kwargs)
        self.layout_root = ScrollView(do_scroll_x=False, do_scroll_y=True, size_hint=(1, None))
        self.layout = BoxLayout(orientation='vertical', size_hint=(1, 1))
        self.lbl1 = Label(text=self.total_training_sessions_text)
        # Кнопка, при нажатии которой откроется второй экран
        self.btn_create = Button(text='Создать Шаблон', on_press=partial(app.change_screen_manager, 'Second')) #Don't mind this. The partial function doesn't work
        # self.btn_create.bind(on_press= изменить sm.current на второй экран)
        self.lbl2 = Label(text='Шаблоны:')  # , pos_hint={'x': -0.42}

        self.layout.add_widget(self.lbl1)
        self.layout.add_widget(self.btn_create)
        self.layout.add_widget(self.lbl2)

        import os
        for filename in os.listdir('templates'):
            with open(os.path.join('templates', filename), 'r', encoding='utf-8') as file:
                self.lbl_name = Label(text = str(filename.replace('.txt', '')))
                self.layout.add_widget(self.lbl_name)
                k=0 #Считает кол-во упражнений в шаблоне
                while True:
                    exercise_info = file.readlines(2)
                    k+=1
                    if not exercise_info:
                        break
                    num_of_exercise, exercise = exercise_info
                    num_of_exercise = str(num_of_exercise.replace("n", ""))
                    exercise = str(exercise.replace("n", ""))
                    text_1 = str(k) + " - " + exercise + " x" + num_of_exercise
                    self.template_lbl = Label(text = text_1)
                    self.layout.add_widget(self.template_lbl)
                self.template_btn = Button() # will actually make the button when the problem is fixed
                    




        self.layout_root.add_widget(self.layout)
        self.add_widget(self.layout_root)
    def create_widgets(self):
        for template in self.templates:
            pass



class SecondScreen(Screen):
    def __init__(self, **kwargs): # add template
        super(SecondScreen, self).__init__(**kwargs)
        self.create_widgets() #ТОЖЕ УБРАТЬ

    def create_widgets(self):#, template):

        # for x in template.keys():
        #    name = str(x)
        name = 't1'
        layout_root = ScrollView(do_scroll_x=False, do_scroll_y=True, size_hint=(1, None))
        layout = BoxLayout(orientation='vertical')
        lbl1 = Label(text=name)
        btn_rest = Button()
        btn_start = Button()
        # btn_cancel = CancelButton()
        # self.btn_cancel = Button(text='Отмена', on_press=app.sm.switch_to('First'))
        # self.ids['cancel'] = Button()
        # self.ids['layout'].add_widget(self.btn_start) НЕ РАБОТАЕТ
        # self.ids['layout'].add_widget(self.btn_rest)
        layout.add_widget(lbl1)
        layout.add_widget(btn_rest)
        layout.add_widget(btn_start)
        # layout.add_widget(btn_cancel)
        layout_root.add_widget(layout)
        self.add_widget(layout_root)




class ThirdScreen(Screen):
    def __init__(self, **kwargs):
        super(ThirdScreen, self).__init__(**kwargs)
        self.layout_root = ScrollView(do_scroll_x=False, do_scroll_y=True, size_hint=(1, None))
        self.layout = BoxLayout(orientation='vertical')
        self.name_input = TextInput(text='Название Шаблона', multiline=False, size_hint = (0.8, None), height='100dp')


class FourthScreen(Screen):
    def __init__(self, **kwargs):
        super(FourthScreen, self).__init__(**kwargs)


class FifthScreen(Screen):
    def __init__(self, **kwargs):
        super(FifthScreen, self).__init__(**kwargs)

if __name__ == '__main__':
    app = YogaApp()
    app.run()

I have tried giving pos_hint = {‘top’: 1} to the first widget. Didn’t work (probably should have expected that)
I thought that the BoxLayout doesn’t occupy all of the space of the ScrollView, so I have given the BoxLayout size_hint = (1,1), but it didn’t work

I have not tried anything else because I have no idea what’s wrong with it