Bulk Bunny doesn't impose any limit on how many discount codes you can create. However, Shopify does have a limit of 20,000,000 codes in total per store.
This means that you won't be able to create more than 20,000,000 discount codes per batch, per discount or in total across all discounts.
For more details on the limits and restrictions imposed by Shopify please refer to the official Shopify help article.