The application menus (like File, Edit, etc) had a built-in way of detaching them when they were expanded so that you could keep them open and place them somewhere convenient on your screen. This was useful if you had to select different menu options frequently.

here you go

https://tkdocs.com/images/tearoff.png

this used to be on by default in IDLE-python, but it seems they disabled it in more recent versions

you clicked tat dotted line and the menu detached and you could place it anywhere you wanted