I have congenital flat feet, and I discovered that not only are my ankles involved, but the knees also. One of my knees turns inward, which contributed to a problem I had with skiing. It wasn’t until after I got my ski boots canted that I was able to successfully ski in powder. Interesting that the podiatrist and sports medicine doctors missed that.
Once your arches are flat, you will harm yourself to try to make them go back by wearing an arch support higher than your foot will tolerate. I did this, not realizing that the shoe I had bought had too high an arch, and nearly crippled myself for a while. What you want is to support the arch you have left. In my case I’m very happy with one from Profoot that is designed for people with flat feet and it molds to the shape of my foot. I also cannot wear high heels safely or comfortably.
If you do buy an arch support, make sure you remove the one that came with the shoe you want to wear. Some shoes have a built in arch support which cannot be removed, so be careful what you buy. I don’t know about running shoes, but you might see if you can find one that will allow you to put in your own arch support. If so, be sure to try it on with the new one inside before you buy.