Kivy + multiprocessing throws a TypeError - python-3.x

Question

Can someone explain why multiprocessing works so weird with kivy?
Minimum example:
from kivy.app import App
from kivy.uix.button import Button
from multiprocessing import Process
class myApp(App):
def f(self):
print('test')
def test(self, caller):
pr = Process(target=self.f)
pr.start()
def build(self):
btn = Button(text='Go')
btn.bind(on_press=self.test)
return btn
if __name__ == '__main__':
myApp().run()
I get the following error:
Traceback (most recent call last):
File "/Users/eab06/Desktop/WJB/PythonProjects/Boring Button/test.py", line 20, in <module>
myApp().run()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/app.py", line 950, in run
runTouchApp()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/base.py", line 582, in runTouchApp
EventLoop.mainloop()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/base.py", line 347, in mainloop
self.idle()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/base.py", line 391, in idle
self.dispatch_input()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/base.py", line 342, in dispatch_input
post_dispatch_input(*pop(0))
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/base.py", line 248, in post_dispatch_input
listener.dispatch('on_motion', etype, me)
File "_event.pyx", line 709, in kivy._event.EventDispatcher.dispatch
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/core/window/__init__.py", line 1412, in on_motion
self.dispatch('on_touch_down', me)
File "_event.pyx", line 709, in kivy._event.EventDispatcher.dispatch
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/core/window/__init__.py", line 1428, in on_touch_down
if w.dispatch('on_touch_down', touch):
File "_event.pyx", line 709, in kivy._event.EventDispatcher.dispatch
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/kivy/uix/behaviors/button.py", line 151, in on_touch_down
self.dispatch('on_press')
File "_event.pyx", line 705, in kivy._event.EventDispatcher.dispatch
File "_event.pyx", line 1248, in kivy._event.EventObservers.dispatch
File "_event.pyx", line 1172, in kivy._event.EventObservers._dispatch
File "/Users/eab06/Desktop/WJB/PythonProjects/Boring Button/test.py", line 11, in test
pr.start()
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/process.py", line 121, in start
self._popen = self._Popen(self)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/context.py", line 224, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/context.py", line 283, in _Popen
return Popen(process_obj)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 32, in __init__
super().__init__(process_obj)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_fork.py", line 19, in __init__
self._launch(process_obj)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/popen_spawn_posix.py", line 47, in _launch
reduction.dump(process_obj, fp)
File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/reduction.py", line 60, in dump
ForkingPickler(file, protocol).dump(obj)
File "stringsource", line 2, in kivy._event.EventDispatcher.__reduce_cython__
TypeError: no default __reduce__ due to non-trivial __cinit__
The thing is, I swear I got this to work an hour ago, but I changed some things and forgot to fork. Any help/explanation would be appreciated.