I had not considered instant mashed potatoes as a kind of flour, but now a whole set of possibilities are open.
Now I wonder if you could mix with real flour and make a kind of potato bread like that.
Just saw your response.
I can answer that question. Im a professional Baker, by trade.
You can absolutely use Instant taters in bread dough. I occasionally offer it for sell, in my business. Sometimes I offer it in "Sammich Bread", sometimes in Buns, or Rolls. Sometimes whole unsliced loaves.
Instant Potatoes help bread to hold onto moisture, offering a longer shelf life. Also, brings a sort of earthiness to the flavor profile. I prefer the Walmart Great Value brand. They have no off taste, and are dirt cheap. They come in a brown box. At my local Walmart, they are in the Ethnic Section. Beats me as to why.. Bobs Red Meal offers actual Potato Flour. Its nearly the exact same thing for 3 times the money. God Bless Capitalism.

I work in metric, so you would have to experiment. But, I usually use about 20% potatoes, by weight. So that translates to approx. 1/3 cup instant potatoes substituted for about 3 tbsp. flour. So, measure out your flour by scooping it into the measuring cup, then take out about 3 tbsp. Then put in, 1/3 cup potatoes. Thats for every cup of flour in your recipe.
Or, just by a cheap set of kitchen scales that measure in metric, from Wally World.

Moisture. The potatoes suck up the water in your dough. You will most definitely have to add more water. I usually make 8 loaves at once in the mixer, (20 quart) so I add the potatoes in little by little so the dough doesnt seize up. But I assume you would be making 1 loaf at a time, in something like a KitchenAid. You should have no problems. Just keep some extra water to drizzle in if needed.
If I can be of further assistance, dont hesitate. I can share a couple recipe's if you like as well.