In this study, we demonstrate through combined density functional theory (DFT) simulations and experiments that integrating nitrogen-doped graphdiyne (N-GDY) into a multimetal Fe-Co-La amorphous (oxy)hydroxide aerogel synergistically enhances its catalytic performance for the oxygen evolution reaction (OER). DFT calculations reveal that pyridinic nitrogen sites on the N-GDY support modulate the electronic structure of Fe-Co-La active sites, shifting the metal d-band centre to around –1.31 eV. This electronic tuning optimizes intermediate adsorption energies and thereby lowers the theoretical overpotential for OER. Structurally, the N-GDY scaffold induces local crystallization within the amorphous aerogel network, templating the growth of ~5–10 nm nanocrystalline domains inside the otherwise amorphous matrix. These in situ nanodomains create defect-rich active interfaces, leading to improved overall activity and durability. As a result of these electronic and structural synergies, the optimized N-GDY/Fe-Co-La composite requires only 219 mV overpotential to reach 10 mA cm⁻² (337 mV at 100 mA cm⁻²) and exhibits a Tafel slope of ~51 mV dec⁻¹. It also maintains high OER activity over 240 hours of continuous operation with minimal performance decay, demonstrating excellent long-term durability. These findings highlight the potential of rationally coupling high-entropy amorphous oxide frameworks with tailored carbon supports as a promising route toward scalable, high-performance water-splitting catalysts.