  Moir\'e materials represent strongly interacting electron systems bridging
topological and correlated physics. Despite significant advances, decoding
wavefunction properties underlying the quantum geometry remains challenging.
Here, we utilize polarization-resolved photocurrent measurements to probe
magic-angle twisted bilayer graphene, leveraging its sensitivity to the Berry
connection that encompasses quantum "textures" of electron wavefunctions. Using
terahertz light resonant with optical transitions of its flat bands, we observe
bulk photocurrents driven by broken symmetries and reveal the interplay between
electron interactions and quantum geometry. We observe inversion-breaking
gapped states undetectable through quantum transport, sharp changes in the
polarization axes caused by interaction-induced band renormalization, and
recurring photocurrent patterns at integer fillings of the moir\'e unit cell
that track the evolution of quantum geometry through the cascade of phase
transitions. The large and tunable terahertz response intrinsic to flat-band
systems offers direct insights into the quantum geometry of interacting
electrons and paves the way for innovative terahertz quantum technologies.
