Altermagnets exhibit spin-split band structures without net magnetization, offering a promising platform for unconventional spin transport and multiferroic phenomena. Based on symmetry analysis and first-principles calculations, $\mathrm{VO}{X}_2$ $(X=\text{Cl,}\text{Br,}\text{I})$ monolayers are identified as two-dimensional ferroelectric altermagnetic multiferroics, in which spin splitting is precisely tunable by switching either ferroelectric polarization or the Néel vector. Notably, the noncentrosymmetric altermagnetic structure of ${\mathrm{VOI}}_2$ gives rise to a giant, magnetically reversible bulk spin photovoltaic effect. Crystal symmetry enables a decoupling between spin and charge shift currents, allowing the generation and independent control of pure spin and pure charge photocurrents. These responses serve as internal readout mechanisms of the four ferroic multistates, enabling programmable switching via electric, magnetic, or optical fields. Our findings establish a general design strategy for nonvolatile multistate memory and nonlinear optospintronic devices based on two-dimensional multiferroics with symmetry-enabled spin-charge disentanglement.

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• Ferroelectric phase transition
• First-principles calculations
• Magnetoelectric effect
• Optical conductivity
• Shift current
• Spin current
• Altermagnets
• Electronic structure
• Layered crystals
• Multiferroics
• Nanostructures
• Noncentrosymmetric materials
• Peierls transition