<p>We explore the dynamics of modulational instability (MI) in PT-symmetric fiber Bragg gratings (FBGs), with a focus on four-wave mixing (FWM) as an intermodulation process. While FWM has been extensively analysed in traditional media, its role within PT-symmetric FBGs warrants further investigation. Adding equal amounts of gain and loss to the fundamental components of the PT-symmetric concept yields interesting new results. Furthermore, we investigate how nonlinear saturation affects MI in the structure of FBG. Using a modified saturable nonlinearity (MSN), we investigate modulation instability and observe a variety of unusual MI spectra under different conditions, spanning the transition from the traditional operating regime to the wrecked PT-symmetric phase. These features are obtained by introducing weak perturbations superimposed on continuous-wave or pulse backgrounds and analysing their linear stability. Among the resulting spectra, a particularly striking MI structure emerges, consisting of two oppositely tilted cone-like formations. Additionally, we investigate the impact of key system characteristics across two essential areas: ordinary and abnormal spreading scenarios, including loss, gain, and pump power, saturable nonlinearity, and self-phase modulation. In particular, we find that, regardless of the independent effects of system characteristics, the influence of nonlinear saturation improves MI spectra across all domains. Lastly, our MSN can regulate the instability domain, which is helpful for the formation of solitary waves and solitons in the system described above. Due to its stability and ability to travel great distances without dispersing, the soliton has a wide range of applications in physics, engineering, and biology. One of these uses is in nonlinear optics for optical communications.</p>