Yes, if the Python runtime caches file names and determines based on the cache whether a file exists, then it needs to normalize both the file names in the cache and the name of the file it’s looking for. As far as I know, both HFS and APFS do this themselves when asked for a file by name, but if you ask for a list of available files, they don’t know what you’re comparing against.

I don’t think codecs would be involved here; I’d use unicodedata.normalize with either NFC or NFD – doesn’t matter which one.