Ballet flats really are a specific shoe style influenced from the footwear used by ballet. By design these shoes are extremely minimalist. They do not much for the foot except cover it and come in a wide array of good looking designs. Additionally they are likely to be rather snug fitting to help the footwear stay on the feet. There isn't anything fundamentally wrong with these types of shoes so long as they are fitted properly and they are of the right size for the feet.
The challenge using these minimalist categories of footwear is should there be a foot condition that will require some sort of mid-foot support, even on a short-term time frame. The key sorts of problems that this might be needed are especially if you are on your feet all day and the feet and legs get very fatigued. As a result of the minimal character with the style plus the usually snug fitting of the shoes, there isn't going to be a lot of room inside the footwear to do a lot. Medically, choices or solutions may be restricted for those who spend the majority of your time in this sort of footwear. There is hardly any way that a regular foot supports will probably go with these types of shoe. Occasionally a trimmed down foot orthoses just might fit into the footwear. In other cases the problem can be handled by changing to another type of shoes that foot orthoses could be easily used in for short period until the issue gets better. It is always best to see a podiatrist and go over your options you have should you really do need some sort of support and if it may be accommodated with your ballet flats style footwear.
You will find a very limited variety of ballet flats that can be purchased which do have arch support type variations included in the footwear. Nevertheless, they are hard to find and might not be ideal for you. You can find the instant arches styles of self adhesive pads that may be stuck inside the footwear to give some kind of support and that is often a reasonable solution if that is what is needed to manage the issue. Podiatry practitioners do use them sometimes if you have hardly any other more suitable alternatives which will get support in a ballet flat type of footwear.