Hello and welcome to the forum.
Potatoes are not toxic, but they are not really a good tortoise food either. A small amount of grated potato mixed in with a big pile of greens once in a while won't hurt anything, but why? There are other, better things to feed your tortoise.
What species are you feeding?
Is this cooked sweet potato? My iguanas like it, and yam and manioc too, cooked and mixed occasionally with their regular green diet. I have not tried my tortoises with potato, but if I did I would cook it first. I think raw irish potato may not be good to feed anything.I feed my Redfoot sweet potato from time to time.
Uncooked, I usually just grate it with like a cheese grater and mix it with some greens.Is this cooked sweet potato? My iguanas like it, and yam and manioc too, cooked and mixed occasionally with their regular green diet. I have not tried my tortoises with potato, but if I did I would cook it first. I think raw irish potato may not be good to feed anything.