I have to preface by saying that this isn’t really related to Home Assistant. I can’t find a more generic home automation community on Lemmy and I figured someone here might have some experience with this so I hope is post is allowed.
I have a large masonry fireplace that I’m fixing some issues with. It has a fresh air intake that I’m venting outside the house. Code says the air intake also has to have a damper which can be closed to prevent the fire from burning out of control.
I’m planning to use a 24 volt power open/power close damper. I want to be able to modulate it with a wall control where it can be set in increments somewhere between 0% and 100% open. I’m sure I could engineer a creative solution but I wanted to see if anyone else had a simpler way of accomplishing this first.
I know those kind of motorized vents are used in commercial HVAC. (Here’s a white paper on a stepper motor for one https://www.portescap.com/en/newsroom/whitepapers/2021/10/customized-and-reliable-stepper-motors-for-damper-applications )
A stepper would be the easiest thing because if you know it takes 10 steps to fully open from fully closed, you could keep track of how many steps you have sent each direction in Home Assistant and be able to display the current status. 
If you want a knob on the wall that controls this, I think somewhere behind it you are still going to need a control system that translates wall switch inputs into stepping logic. Home Assistant would be able to do that easily.