Okay, I looked up your supplement and it does not have the dreaded useless Magnesium oxide in it. So it should work for you.
Many combo products do have this in it and people count on it working and it doesn't.

The link works for me if you click on it. (don't copy paste it).

Yes, if you have magnesium in a topical form (this is becoming more common today), I'd rub some on. I'd check your label for it and see how much is in there. If it is like 100mg/gram, you can cut back on the oral magnesium while you use the topical.

The usefulness of the magnesium is to open the blood vessels up that are constricted by the inflammatory compounds called cytokines. When the little blood vessels constrict, metabolic byproducts build up and nutrients and oxygen cannot get thru either. So the inflammation sort of cycles on itself and doesn't go away.

I found Lidoderm patches very useful (and I still use them) for nerve pain. These are RX only. 1/2 of a patch is enough for one foot. Placed properly they can block the nerve signals and give relief. I found that for my meralgia paresthetica I had for many years after my c-section, the nerve actually stopped firing after 14 consecutive days use, and I went into a remission!

For your foot problems I'd place the patch above the area where the surgery was done. (around the ankle). This may work for you. Interrupting the nerve on its way to the spine, is better than putting the patch over where you feel the pain.

Also I'd caution about heat. Heat will activate nerve pain and make it worse, IMO. My MP will activate again in steam rooms, or hot baths. So I have to be careful with heat..

My chiro who is very good, cautions against excessive heat --she is the one who steered me clear of it.

Some people like menthol containing rubs which can minimize burning. I like Biofreeze, but others here use their favorite type like IcyHot.
Biofreeze has Ilex in it which is a powerful antioxidant, and I was given it during some PT for a tendon injury. I use it on my feet now when I have alot of burning (which comes and goes).

If you don't have discoloration with your foot pain, or swelling, that is a good sign.

Pronation is a big cause of foot pain. My son had that too in one foot when he went to college . The sudden long distances he had to walk all day, from class to class really started an acute pain in his right foot. I took him to a good podiatrist who found nothing "wrong" in the ankle, and a set a orthotics fixed the problem. He still will get twinges jogging, so he gave that activity up, and now has an elliptical in his basement instead.
Ellipticals are far better and less stressful on the feet than
treadmills!

I have to say, after all your pregnancies your body may be just reacting to that stressor.
You know when a woman is pregnant, and for a time after, the body makes a hormone called relaxin. This relaxes the tendons and makes them more stretchy, and loose. This is mostly for the
pelvic tendon so that delivery of the head is possible for the baby. But relaxin relaxes everything, and stress injuries are possible in some women who may have excess of this hormone.
Relaxin has been linked to fibromyalgia (patients seem better during pregnancy). But relaxin increases 10 times in pregnant women, and may loosen joints in some more than others. Low back pain has been linked to it according to some medical sites.
I do know that most women change shoe sizes after pregnancy and that may be due to loosening of the bones in the foot and the swelling pregnancy may bring.

The foot is really complicated. Here is a good site showing anatomy! Using these pictures helps to place Lidoderms BTW.
Scroll down and the nerves in the foot are shown in yellow.
This site also gives alternate ways to lace your shoes if you have a high instep. (this was helpful to me too)
https://www.northcoastfootcare.com/f...t-anatomy.html
https://www.northcoastfootcare.com/footcare-info.html