<p>This study investigates the multifield vibration behavior of a porosity-dependent bidirectional functionally graded piezoelectric nano-plate (FGPN) subjected to hygrothermal and thermoelectric loading. The material composition is defined by sigmoid and power-law distributions along both transverse and axial directions, accommodating even, uneven, and symmetrically centered porosity patterns. The model incorporates nonclassical elasticity theory and von Kármán nonlinear strains, with the governing equations formulated using a modified first-order shear deformation theory and derived through the energy principle. A higher-order finite element formulation, coupled with a modified Newton-Raphson procedure, ensures robust computational accuracy, validated through convergence tests. The analysis delves into the influence of porosity distribution, bidirectional material variations, non-uniform thickness, thickness ratios, variable elastic foundations, and boundary conditions on vibrational behavior. Additionally, the study explores the interplay of hygrothermal and electrical loading conditions in diverse configurations. The findings highlight the pivotal role of bidirectional material gradation in shaping the vibrational response of porous FGPN structures, offering valuable insights for the design of nano-plates in hygrothermal and thermoelectric applications.</p>