Consideration how electrons move through molecular junctions will enable researchers to create superior thermoelectric energy conversion materials. This research applies density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) formalism to study the electronic and thermoelectric behavior of metalloid-endohedral fullerenes (M@C₈₀, M = P, S, As, Se) connected to gold and graphene electrodes. The transmission coefficient T(E) undergoes significant changes when metalloids are introduced into C₈₀, which creates unique electronic transport characteristics. Metalloid-doped systems achieve notable improvements in thermoelectric response and performance metrics like the Seebeck coefficient (S) and figure of merit (ZT), especially when integrated with graphene electrodes. Se@C₈₀ surpasses all other dopants in terms of thermal conductance and thermoelectric performance across both tested electrode types. Doping with metals is critical since it is important to change electronic transport properties and improve thermoelectric efficiency, which provides useful information for developing new molecular electronics and nanoscale energy conversion devices.