<p>This study employs the Separate Spin Evolution Quantum Hydrodynamic Model (SSE-QHM) to explore the influence of quantum effects—namely the Bohm potential, exchange interaction, and spin polarization—on the nonlinear dispersion properties and modulational instability growth rates. The analysis focuses on high-frequency Quantum Upper Hybrid Waves (QUHWs) and their nonlinear coupling with Quantum Lower Hybrid Waves (QLHWs), Quantum Ion Cyclotron Waves (QICWs), and Quantum Alfvén Waves (QAWs) in a magnetized quantum electron-ion plasma. Using the standard phasor matching technique, we derive nonlinear dispersion relations for these coupled wave modes, shedding light on three-wave interactions and modulational instabilities. Parametric analysis indicates that instability growth rates are highly sensitive to pump wave frequency, Bohm potential, exchange correlation, and spin polarization. Notably, spin polarization enhances instability growth at shorter wavelengths, whereas at higher wave numbers, the Bohm potential and exchange correlation suppress instability, promoting wave stabilization. Additionally, the growth rates of three-wave decay instability decrease with increasing quantum effects, underscoring the significant role of quantum corrections in wave propagation and instability thresholds. These findings advance the theoretical understanding of quantum plasma dynamics and have important implications for astrophysical plasmas, quantum magnetohydrodynamics, and emerging plasma-based quantum technologies.</p>