Why Does a Balloon Stick to a Wall After Being Rubbed on Hair?

When a balloon is rubbed on hair, repeated contact and separation transfer electrons from one material to the other. The balloon acquires a net charge and the hair is left with the opposite charge. Friction has not created charge; it has redistributed charge that was already present.

The wall remains electrically neutral overall, so why is it attracted? As the charged balloon approaches, the distributions of charge in the wall’s atoms and molecules shift very slightly. Charge opposite to the balloon moves a little closer, while like charge is displaced a little farther away. This is polarisation. Because electrostatic force weakens with distance, the attraction from the nearer opposite charge is stronger than the repulsion from the farther like charge. The resulting net force can hold the light balloon against the wall.

Charging and polarisation are different. The balloon has a net charge; the wall usually has only a small separation of positive and negative charge while remaining neutral overall. When the balloon eventually falls, gravity has not suddenly increased. Charge has gradually leaked away through the air, a hand or the wall, weakening the attraction; humid air usually speeds that leakage.

https://openstax.org/books/physics/pages/18-1-electrical-charges-conservation-of-charge-and-transfer-of-charge
https://phet.colorado.edu/en/simulations/balloons-and-static-electricity