What is the temperature of the star F Cygni?

There is no star with the "F Cygni" classification since there is no exact Greek letter correlation.

Zeta Cygni A is an expanding star with three times the mass of the Sun and 15 times its radius, and radiating at 112 times the Sun's brightness. It is fusing helium and has a surface temperature of about 4910 K (compared to 5778 K for the Sun).

Gamma Cygni (Γ Cygni, aka Sadr) is an even larger star, a supergiant, 12 times the Sun's mass, 150 times its radius, and emitting 33,000 times as much energy. Its surface is only 6100 K, close to the Sun's 5778 K but with a much faster rate of change. It may only last a few million years in its current state.