Or perhaps the bytearray can be converted to a bytes object. This is not optimal performance-wise but is unlikely to make a difference in real-world code (if you are passing a filename to an external API, chances are some IO will occur which will dwarf the cost of creating a separate bytes object).
But I agree that supporting bytearrays in filename-taking functions, while "nice" from a consistency point of view, isn't really useful in practice. So I would be ok to remove that support if it simplifies (or avoids complexifying) the logic for those functions.