In the era of precision measurements of the neutrino oscillation parameters, upcoming neutrino experiments will also be sensitive to physics beyond the Standard Model. ORCA is an atmospheric neutrino detector currently being built at the bottom of the Mediterranean Sea, that will measure atmospheric neutrino oscillation parameters with high precision and probe new physics at GeV energies. The final ORCA configuration of 115 string-like vertical detection units will be able to probe several theories beyond the Standard Model in neutrino physics. In this work, a three-flavour neutrino oscillation scenario in which the third neutrino mass state, $\nu_3$, decays into an undetectable state, e.g., a sterile neutrino, is investigated with the first configuration of ORCA with six detection lines, ORCA6. A refined high-purity neutrino sample corresponding to 433 kton-years of data taking has been analysed and optimised for the search of this phenomenon. This contribution presents the bounds obtained in the decay parameter, $\alpha_3=m_3/\tau_3$, and future sensitivity perspectives with ten years of data taking with the future ORCA configuration of 115 detection units.