[Tkinter] How to add multiple frames to main window

[Riddle]

I am at a loss. If I run that exact same code, it works with no errors.

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Did you try to copy and paste my code into a new file, just to see if it works? Maybe it is a minor difference in code that you are missing.
Also, I doubt that it matters, but I am using Version 3.8.2 of Python.