A novel Ga₂TeS monolayer with a diamondene-like structure is investigated using DFT + G₀W₀ + BSE calculations to explore its stability, transport, and electro-optical properties under biaxial strain. The monolayer exhibits dynamical and thermal stability, high electron mobility (>2000 cm²·V⁻¹·s⁻¹), a moderate direct bandgap, and excellent light absorption. Under biaxial strain, the bandgap is tunable, electron mobility improves, and visible-light absorption significantly increases. These properties suggest that Ga₂TeS is a promising optoelectronic material. Group-III monochalcogenides (MX) are 2D materials with excellent properties and applications in spintronics, photovoltaics, and photocatalysts. Theoretical studies have predicted indirect semiconductors with wide bandgaps. Janus structures, such as MoSSe and WSSe, have been synthesized, and their properties have been studied. The M₂XY monolayers, including Ga₂STe, Ga₂SeTe, In₂STe, and In₂SeTe, have moderate direct bandgaps and excellent optical and electronic properties, making them suitable for optoelectronic applications. Previous studies have focused on Janus M*XY and M₂XY monolayers. However, the isomer Ga₂TeS monolayer has not been studied extensively, and its strain effects are unexplored. The Ga₂TeS monolayer's structure is similar to experimentally fabricated diamondene. Many-body interactions are crucial for 2D materials due to enhanced electron-electron and electron-hole couplings, which affect their electro-optical properties. In this study, the Ga₂TeS monolayer is systematically analyzed using DFT and many-body perturbation theories. The strain effects on its stability, electronic, transport, and optical properties are investigated. The carrier mobility is calculated using the effective mass approximation and deformation potential theory. The electronic band structure is corrected using the G₀W₀ method. Phonon dispersions are obtained using density functional perturbation theory. The thermal stability is examined via finite-temperature molecular dynamics simulations. The results indicate that Ga₂TeS is a promising optoelectronic material with tunable properties under strain.A novel Ga₂TeS monolayer with a diamondene-like structure is investigated using DFT + G₀W₀ + BSE calculations to explore its stability, transport, and electro-optical properties under biaxial strain. The monolayer exhibits dynamical and thermal stability, high electron mobility (>2000 cm²·V⁻¹·s⁻¹), a moderate direct bandgap, and excellent light absorption. Under biaxial strain, the bandgap is tunable, electron mobility improves, and visible-light absorption significantly increases. These properties suggest that Ga₂TeS is a promising optoelectronic material. Group-III monochalcogenides (MX) are 2D materials with excellent properties and applications in spintronics, photovoltaics, and photocatalysts. Theoretical studies have predicted indirect semiconductors with wide bandgaps. Janus structures, such as MoSSe and WSSe, have been synthesized, and their properties have been studied. The M₂XY monolayers, including Ga₂STe, Ga₂SeTe, In₂STe, and In₂SeTe, have moderate direct bandgaps and excellent optical and electronic properties, making them suitable for optoelectronic applications. Previous studies have focused on Janus M*XY and M₂XY monolayers. However, the isomer Ga₂TeS monolayer has not been studied extensively, and its strain effects are unexplored. The Ga₂TeS monolayer's structure is similar to experimentally fabricated diamondene. Many-body interactions are crucial for 2D materials due to enhanced electron-electron and electron-hole couplings, which affect their electro-optical properties. In this study, the Ga₂TeS monolayer is systematically analyzed using DFT and many-body perturbation theories. The strain effects on its stability, electronic, transport, and optical properties are investigated. The carrier mobility is calculated using the effective mass approximation and deformation potential theory. The electronic band structure is corrected using the G₀W₀ method. Phonon dispersions are obtained using density functional perturbation theory. The thermal stability is examined via finite-temperature molecular dynamics simulations. The results indicate that Ga₂TeS is a promising optoelectronic material with tunable properties under strain.