In searching this SE, I see many questions discussing traditional ceiling fans and dimmer switches.
This question revolves around bathroom in-wall exhaust fans and dimmer switches. Is it safe to replace a standard on/off switch with a dimmer switch for an in-wall bathroom exhaust fan? Will doing so quickly destroy the fan?
The fan is a standard construction-grade inexpensive in-wall exhaust fan.
The idea is to conserve energy and reduce fan noise.
After my mother-in-law cooks a meal, it can be turned up to full power in order to handle the increased noxious vapors in the bathroom due to all the urgent visits. Otherwise, it can be used at lower levels.