Conventional spectroscopic techniques often provide limited insight into the complex carrier dynamics of multilayer semiconductor devices under operational conditions. Although time-resolved photoluminescence (TRPL) measurement is widely used to monitor carrier dynamics in a perovskite film, interpreting carrier dynamics under operating conditions remains a critical challenge due to competing processes, including surface and bulk recombination, carrier transfer to the charge transport layers (CTL), carrier trapping and detrapping, capacitive charging and discharging. Understanding the interplay among these processes is crucial for optimizing charge collection, minimizing recombination losses, and enhancing photodetector device performance. In this work, we have investigated operando carrier dynamics of a 2D Ruddlesden-Popper mixed-halide perovskite (Cs₂PbBr₂I₂) photodetector using simultaneous TRPL and photocurrent measurements under pulse laser and LED illumination with varied wavelengths. A pulse laser is used as an excitation source for TRPL, while a CW LED with different wavelengths is used to modify the carrier population and trap occupancy during device operation. The impact of CTLs (TiO₂ and CuI) on carrier extraction or interfacial transport was initially confirmed by PL and TRPL measurements, which exhibited strong quenching, indicating efficient carrier transfer through the transport layers. The operando measurements reveal that photocurrent and decay lifetime are strongly dependent on the wavelength and intensity of the background illumination, demonstrating that trap occupancy and interfacial charge extraction affect the measured carrier dynamics and device performance. Furthermore, bias-dependent TRPL measurements under short-circuit and forward bias also show a significant decrease in the carrier lifetime, accompanied by an increase in photocurrent, indicating improved charge extraction in the device. These observations underscore the role of carrier trapping, detrapping, recombination, and carrier extraction processes in an operating device. This work demonstrates operando TRPL as a powerful tool for unraveling the interplay between carrier recombination, trapping, and charge extraction in multilayer perovskite photodetectors, providing a more reliable interpretation of carrier dynamics in a working device.