def is_fancy_indexer(indexer: Any) -> bool:
    """Return False if indexer is a int, slice, a 1-dimensional list, or a 0 or
    1-dimensional ndarray; in all other cases return True
    """
    if isinstance(indexer, int | slice):
        return False
    if isinstance(indexer, np.ndarray):
        return indexer.ndim > 1
    if isinstance(indexer, list):
        return bool(indexer) and not isinstance(indexer[0], int)
    return True
Return False if indexer is a int, slice, a 1-dimensional list, or a 0 or
    1-dimensional ndarray; in all other cases return True
    
xarray/core/indexing.py