A sensor converts a non-electrical measurement to a (commonly electrical) signal representing it. An actuator converts a (commonly electrical) signal to a physical effect.
For a potentiometer to be a "pure" electrical sensor, you'd put a constant voltage across its track and pick of a voltage representing the position from the wiper. While this is increasingly done in a manner as simple as that (and has the advantage to be comparatively robust against noise and crackling when changing the position), at least classical designs make potentiometers have a more complex role in a circuit, like being part of a voltage divider working on an AC signal.
There are complex in-between things: for example, a relais (or optocoupler) does not function as an actuator unless you split it into its constituent components or view it through the lens of creating noise or magnetic fields. A quartz crystal is neither sensor nor actuator even though it works through mechanical vibration (and fixating its case may be necessary to ensure reliable operation parameters).
A spark plug is clearly an actuator though its principal effects can be considered electrical.
A resistor is not usually considered an actuator, but a resistor thermically coupled to a crystal oscillator and used as a heating element for stabilising its operating frequency is functioning as an actuator.
So it's all a bit handwavy. But a potentiometer clearly is not an actuator on its own, though a thing like a "motor fader" in a mixing desk controller does contain an actuator component integrated with the potentiometer.