@SebastianChk Is OneDrive involved? There can be issues with users of OneDrive as it stores files actually in different locations than users think. See discussion here.
What you describe sounds like a path issue. You aren’t pointing at the right location. I suspect the directory being the same name is a red herring; however weird bugs do arise. Are you familiar with using ls, %cd, and pwd within a notebook to a navigate your file system and check contents of directories? See here and here links therein. Note that I’m suggesting you start a notebook and do the exploration from within that notebook. That way you’ll assure you see what Jupyter notebook sees and you can compare to what your windows system is telling you.