Bunions: which shoes prevent them?

None. There are no shoes available to prevent a bunion from forming. A bunion is usually due to a biomechaical imbalance in the foot leading to a bunion deformity. A(n) custom orthotic may be of help in controlling the deforming forces leading to a bunion. Once you have developed a bunion the only way to alleviate the bunion is surgical management if it becomes problematic.
With wide toe box. In developing world who wear loose sandals or wear no shoes do not get bunions narrow shoes ( high heels). Are culprits. Shoes with deep wide toe boxes will most likely will prevent bunions but they are not fashionable to wear. !
Use wider shoes. Shoes may not prevent them, but wider shoes may help you walk more comfortably.