Why does condensation form on the wing especially during take-off and landing?
Yes, speed and flaps do make a difference.

The lift created by the wings is approximately constant over the duration of a flight. With full tanks, it is higher at the beginning of the flight, and when the aircraft banks, it is again higher to create the centripetal force for changing its course. But the difference is small¹.

Lift is caused by a pressure difference between the two sides of the wing. In cruise, this difference is low but extends over much of the wing's chord. At low speed, however, the suction on the top surface has a peak right aft of the leading edge, so the maximum suction is bigger than it is in cruise. Exactly this changed pressure distribution causes the humidity to condense, because it lets the air's relative humidity rise above the condensation point. In cruise, the pressure change is lower and the dew point is not exceeded. Also, since the airplane flies slower when close to the ground, the air has more time for the condensation to develop.

See below for a color-coded plot of the speed distribution over a typical airliner airfoil in the landing configuration. Red symbolizes the lowest speed (highest pressure), while purple stands for the highest speeds with the lowest pressure. Such suction peaks must be avoided in cruise to enable the aircraft to fly at a high cruise Mach number.



Airliner airfoil with high lift devices in landing configuration (picture source)

¹ The fuel fraction of airliners rarely exceeds 40%, and the added lift in a 30° bank is only 15%.