Kivy button does not dismiss a popup when it should

Question

I have made a button that when released opens a popup in kivy, which contains a Float Layout. I want the layout to contain a filechooser, so the user can select a folder to save something, and a button that saves this choice and closes the popup at the same time.

I am currently trying to figure out how to make the button close the popup at first. I came up with this code and I really have no idea why it doesn't close the popup, but it doesn't. I don't get any error at all, just nothing happens. The code is this in kvlang:

#:import Factory kivy.factory.Factory

<BoxLayout3>:
    Label:
        text: "Audio:"
        halign: 'center'
        font_size:'20sp'
    CheckBox:


<BoxLayout4>:
    Label:
        text: "Video:"
        halign: 'center'
        font_size:'20sp'
    CheckBox:

<FileWidget>:
    FileChooserIconView:
        id: filechooser
    Button:
        id:my_button
        text: 'Save'
        size_hint: (0.1, 0.1)
        pos_hint:{'x': 0, 'y': 0}
        on_release:Factory.MyPopup().dismiss()

<MyPopup>:
    id:pop
    auto_dismiss: False
    title: "Select a folder"
    FileWidget:



<FloatLayout1>:
    Button:
        text: 'Folder'
        on_release: Factory.MyPopup().open()
        size_hint: None, None
        size: 130, 50
        pos_hint: {'x':0.2,'y':.4}

<FloatLayout2>:
    Spinner:
        id: spinner_id
        text: "Quality"
        values: ['144p', '240p', '360p', '480p', '720p', '1080p', '1440p', '2160p']
        on_text: root.spinner_clicked(spinner_id.text)
        size_hint: None, None
        size: 130, 50
        pos_hint: {'x': .2, 'y':.4}

<BoxLayout2>:
    cols:4
    BoxLayout3:
    BoxLayout4:
    FloatLayout2:
    FloatLayout1:
    





BoxLayout1:
<BoxLayout1>:
    orientation:'vertical'
    cols: 3
    Label:
        text: "YouTube Downloader"
        halign: 'center'
        bold: True
        font_size:'50sp'
    TextInput:
        size_hint: (.5, .2)
        multiline: False
        hint_text: 'Enter the link of the Youtube video you want to download.'
        pos_hint: {"x": 0.25}
    BoxLayout2:
    Button:
        text: "Submit"
        size_hint: (.5, .2)
        pos_hint: {"x": 0.25}

My python code is(it isn't finished yet):

class MyPopup(Popup):
    pass

class FloatLayout1(FloatLayout):
    pass

class FileWidget(FloatLayout):
    pass

class FloatLayout2(FloatLayout):
    def spinner_clicked(self, value):
        pass

class StackLayout(StackLayout):
    pass

class BoxLayout1(BoxLayout):
    pass

class BoxLayout2(BoxLayout):
    pass

class BoxLayout3(BoxLayout):
    pass

class BoxLayout4(BoxLayout):
    pass

class MyApp(App):
    pass