  We investigate the effects of single, multiple, and extended defects in the
form of non-magnetic impurities and vacancies in twisted bilayer graphene (TBG)
at and away from the magic angle, using a fully atomistic model and focusing on
the behavior of the flat low-energy moir\'e bands. For strong impurities and
vacancies in the $AA$ region we find a complete removal of one of the four
moir\'e bands, resulting in a significant depletion of the charge density in
the $AA$ regions even at extremely low defect concentrations. We find similar
results for other defect locations, with the exception of the least coordinated
sites in the $AB$ region, where defects instead result in a peculiar band
replacement process within the moir\'e bands. In the vacancy limit, this
process yields a band structure misleadingly similar to the pristine case.
Moreover, we show that triple point fermions (TPFs), which are the crossing of
the Dirac point by a flat band, appearing for single, periodic, defects, are
generally not preserved when adding extended or multiple defects, and thus
likely not experimentally relevant. We further identify two universal length
scales for defects, consisting of charge modulations on the atomic scale and on
the moir\'e scale, illustrating the importance of both the atomic and moir\'e
structures for understanding TBG. We show that our conclusions hold beyond the
magic angle and for fully isolated defects. In summary, our results demonstrate
that the normal state of TBG and its moir\'e flat bands are extremely sensitive
to both the location and strength of non-magnetic impurities and vacancies,
which should have significant implications for any emergent ordered state.
