In the docs and in the code types, the first argument for repo.index.add() is Sequence[Union[str, os.PathLike, git.objects.blob.Blob, git.index.typ.BaseIndexEntry, Submodule]].
However, actually trying to submit a list of Paths to this argument results in a TypeError, as it seems the code inside _preprocess_add_items does not handle Paths.

I think this could be fixed by changing line 611 inside of _preprocess_add_items in base.py to:

 if isinstance(item, str) or isinstance(item, os.PathLike):