There are currently no mainstream keyboard apps on iOS that have a dedicated comma key, as far as I know. SwiftKey on iOS lacks substantial features, including

There are currently no mainstream keyboard apps on iOS that have a dedicated comma key, as far as I know. SwiftKey on iOS lacks substantial features, including this very basic one. Coupled with the hobbled notification system and the inconsistent back button behavior (sometimes swipe, sometimes top left button, sometimes dedicated home row), the experience on Android is better even if the minor features described in the article are sometimes missing.