Where are you? That looks like the normal seasonal shutdown of a fully herbaceous plant. It is November afterall and in most places in North America, well on the way to winter. Are these plants outdoors or being grown in a greehouse?

I am in Ontario, Canada. However, these plants have been inside my home for the past month or so, where the average temperature is 22C or 71F

Growing dahlias inside the house has the potential for creating all sorts of adverse conditions..........these are not houseplants :-) First would be lack of light. Even with grow lights, you cannot reproduce the intensity and the benefit of real sunlight. Then there would be the lack of humidity that is common to all homes. And both can give rise to all manner of insect issues. Finally, if being grown in a container, these plants will require frequent fertilization.

Can you explain your intent with growing these indoors? At at this time of year?

These plants where on my balcony (I live in an apartment) for all of the summer. I brought them inside in order to keep them green for as long as I could. I did intend to winterize the bulbs eventually, but I thought I'd extend the growing season...

I have a humidifier at home have added fertilizer sticks since I brought them inside. And they were doing fine until a week or two ago...

White patches may indicate a sucking pest other than mites. Look with a magnifier to tell what you have. Usual routine is to let the tops get frosted and then cut back and store, in a cool area. You may not have one in an apartment, where perhaps the only environments available are either fully heated rooms or outdoors on a balcony.