  Isolated flat bands with significantly quenched kinetic energy of electrons
could give rise to exotic strongly correlated states from electron-electron
interactions. More intriguingly, the interplay between topology and flat bands
can further lead to richer physical phenomena, which have attracted much
interest. Here, taking advantage of the recently proposed intertwined Dirac
states induced from the anisotropic coupling between top and bottom surface
states of an antiferromagnetic topological insulator thin film, we show the
emergence of a high-Chern-number (quasi)flat-band state through Moir\'e
engineering of the surface states. Remarkably, the flat bands are isolated from
other bands and located near the Fermi level. Furthermore, topological phase
transitions between trivial and nontrivial flat-band states can be driven by
tuning the out-of-plane electric field. Our work not only proposes a new scheme
to realize high-Chern-number flat-band states, but also highlights the
versatility of the intertwined Dirac-cone states.
