Hidden altermagnetism, characterized by zero net spin polarization but non-zero local spin polarization in two subsystems related by spatial inversion, has recently emerged as a promising route for spintronic and valleytronic applications. Here, using first-principles calculations, we systematically investigate the electronic structure, magnetic properties, and multi-field tunability of hidden altermagnetism in PT -symmetric bilayer V₂SeTeO. We show that the bilayer with a Te-Te interface, possessing PT symmetry, is energetically most stable and exhibits hidden altermagnetism with an overall spin-degenerate band structure, while each individual layer displays pronounced local spin splitting. By applying interlayer sliding, we find that the A′B₁ and A′B₂ stacking configurations induce spontaneous valley polarizations with opposite signs, reaching a valley splitting of 35.5 meV at the valence band maximum, which enables a switchable anomalous valley Hall effect. Furthermore, uniaxial strain along the in-plane direction effectively tunes the valley splitting in the AA stacking, achieving a maximum of 102 meV under 2% compressive strain. In contrast, a perpendicular electric field linearly modulates the spin splitting at both the valence and conduction band edges (up to ~80 meV at 0.06 V/Å), and at higher fields (up to 0.2 V/Å) it drives the system into a nodal-loop semimetallic state protected by mirror symmetry. Additionally, when spin–orbit coupling is included, an in-plane magnetization along the x or y direction breaks the M_xyT symmetry and induces a weak valley polarization of approximately 8–10 meV, whose sign can be reversed by switching the magnetization direction. Our results establish bilayer V₂SeTeO as a versatile platform for the multi-field control of hidden altermagnetism and provide concrete strategies for designing low-power, non-volatile valleytronic and spintronic devices.