Coupling molecular excitations to a quantized radiation field inside an optical cavity produces a set of lightmatter hybrid states known as polaritons. These polariton states, which are a hybridization of matter excitation and photonic excitation, have shown great promise in changing the reactivities of molecules . In particular, the light-matter interaction has been shown to effectively reduce the coupling between excitons and phonons, which is commonly referred to as the polaron decoupling effect. This polaron decoupling effect results in an enhanced charge transfer rate constant, reduction of the homogeneous linewidth of spectra, and causes ballistic exciton-polariton transport. In particular, the exciton-polariton coherence lifetime should be prolonged due to reduced coupling with the phonon bath. Linear 13 and non-linear spectroscopy are powerful measurements that provide a fundamental understanding of the photophysics of polariton systems. Recent theoretical progress has focused on simulating the polariton 2-dimensional electronic spectra (2DES) spectra, such as an analytic expression based on the non-Hermitian Hamiltonian, or based on the Heisenberg-Langevin equation. Nevertheless, there is a lack of general theoretical approaches that can accurately simulate exciton-polariton spectra beyond perturbative methods, with an accurate description of the non-Markovian exciton-phonon coupling and the cavity loss dynamics.