Use the control method specified for the exact mirror and installed driver.
For the legacy Marquee mirrors covered by the linked manual, use the documented normal switched 120 V supply. Do not substitute a line-voltage wall dimmer unless the exact mirror assembly is expressly rated for it.
“LED” does not by itself mean dimmable. Even a driver with separate dimming inputs does not establish compatibility with a household phase-cut wall dimmer. For example, the Mean Well LPF-60D data sheet describes separate low-voltage/PWM/resistance dimming methods; those are different interfaces.
Newer touch-controlled mirror models may have a different control arrangement. Check the model’s own instructions and use its built-in controls as specified. Do not modify internal driver wiring to add a dimming method that is not approved for the complete mirror.
Sources: legacy Marquee manual, Audrey touch-control manual, and the Mean Well LPF-60D data sheet in the related driver article.