This study deals with the instability of shear waves, also known as Kelvin–Helmholtz instability, propagating with a complex frequency ”ω” in magnetically quantized dense gyro-viscous plasmas. The instability arises from the transverse spatial shear of the streaming velocity, which evolves from the DC electric and magnetic fields. In dense plasmas, quantum effects contribute through magnetically quantized statistical Fermi pressure, tunnelling potential and exchange-correlation potential. The contribution of the shear profile, the drift velocity, the number density of medium species, the dc magnetic field and the propagation angle θ of the wavevector on the instability is pointed out analytically as well as graphically. By varying the angle, shear size and density of plasma particles, the growth rate is enhanced. It does not, however, change as the streaming speed increases. This work seeks applications to study the characteristics of complex media like astrophysical and semiconductor plasmas [R. P. Drake, “Hydrodynamic instabilities in astrophysics and in laboratory high-energy–density systems,” Plasma Phys. Control. Fusion, vol. 47, p. B419, 2005].