One Pinterest business account can only be connected to one website or domain. This means if the business uses 1 website but offers multiple categories then it should ideally only have one account. You can also add a subdomain that is connected to your primary domain to your Pinterest account.
It is only when you have multiple websites then you should have one business account per website/domain. If all your business categories are present on the same website, then you can stick to just one business account for your business.