  When the perpendicular magnetic flux per unit cell in a crystal is equal to
the quantum of magnetic flux, $\Phi_0=h/e$, we enter the 'Hofstadter regime'.
The large unit cell of moir\'e materials like magic-angle twisted bilayer
graphene (MATBG) allows the experimental study of this regime at feasible
values of the field around $20$ to $30$ T. In this work, we report numerical
analysis of a tight-binding model for MATBG at one quantum of external magnetic
flux, including the long-range Coulomb and on-site Hubbard interaction. We
study the correlated states for dopings of $-2,0$ and $2$ electrons per unit
cell at the mean-field level. We find competing insulators with Chern numbers
$2$ and $0$ at positive doping, the stability of which is determined by the
dielectric screening, which opens up the possibility of observing a topological
phase transition in this system.
