There are many type of float switches, some with a moveable weight element that is used to actuate the switch when the float rises up.

Te weight is free to move inside the float.

I much prefer these to the water pressure type switches.

They oft n have a small orifice facing downwards that responds when air pressure in the chamber rises as the water level increase.
The problem with them is that the opening to the chamber has a nasty habit of clogging with debris and preventing the pump from turning on when needed.

Other models have a moving magnet on a float rod that activates a reed switch.

There are pretty good unless the rod get jammed.