That is probably a boilerplate recommendation from other Kia model handbooks. There is little point to it with direct injection as that bypasses the intake valves - so no cleaning benefit. All top tier gas brands and most other stations already have detergent in them anyway. In some other countries, there is no detergent in gas, thus you need additives.
On top of that, there are a good number of high mileage Ioniqs and Niros (over 100K) and no forum reports of gunked up valves or injectors. Save your money.
2018 Kia LX HEV Metal Stream with Advanced Tech