  Recently discovered intrinsic antiferromagnetic topological insulator
MnBi$_2$Te$_4$ presents an exciting platform for realization of the quantum
anomalous Hall effect and a number of related phenomena at elevated
temperatures. An important characteristic making this material attractive for
applications is its predicted large magnetic gap at the Dirac point (DP).
However, while the early experimental measurements reported on large DP gaps, a
number of recent studies claimed to observe a gapless dispersion of the
MnBi$_2$Te$_4$ Dirac cone. Here, using micro($\mu$)-laser angle-resolved
photoemission spectroscopy, we study the electronic structure of 15 different
MnBi$_2$Te$_4$ samples, grown by two different chemists groups. Based on the
careful energy distribution curves analysis, the DP gaps between 15 and 65 meV
are observed, as measured below the N\'eel temperature at about 10-16 K. At
that, roughly half of the studied samples show the DP gap of about 30 meV,
while for a quarter of the samples the gaps are in the 50 to 60 meV range.
Summarizing the results of both our and other groups, in the currently
available MnBi$_2$Te$_4$ samples the DP gap can acquire an arbitrary value
between a few and several tens of meV. Further, based on the density functional
theory, we discuss a possible factor that might contribute to the reduction of
the DP gap size, which is the excess surface charge that can appear due to
various defects in surface region. We demonstrate that the DP gap is influenced
by the applied surface charge and even can be closed, which can be taken
advantage of to tune the MnBi$_2$Te$_4$ DP gap size.
