I understand that different aircraft behave differently when flaps are extended / retracted. Some with flaps extended tend to pitch up, some pitch down. Some pitch up initally slightly, then pitches down more etc etc.
It can be helpful to distinguish between the short term transient effect and the longer term effect on the steady state.
Flaps (unless they are very strange ones!) always increase the lift coefficient for a given angle of attack (measured relative to the
original chord line of the aerofoil). Thus if you want to maintain the same speed in level flight, it will be at a lower nose attitude if the flaps are extended. If the flaps increase drag-to-lift, then the aircraft will slow down, and the AoA may need to increase again, and it will also enter a descent, and I think it's rare that the pitch attitude would exceed the original pitch attitude before flap application.
Transient effects depend on many other factors.