It’s in loads of things. Peanuts, spinach, beans, chocolate, avocados, corn, soy… the list is endless. If someone is really sensitive, they can have problems with high oxalate foods. Some people seem to accumulate oxalates, meaning their problems compound, where others have no problem at all. Biology is weird.

Spinach. Many nuts, e.g. almonds. Many beans (including cocoa but excluding coffee). Well, potatoes!

Spinach. Maybe other leafy vegetables.

Spinach and almonds.