Does Groove work with iOS devices?

Yes.

With iPads & iPhones that have USB-C ports built-in, just connect directly using the supplied USB-C cable and it will automatically be recognized and work.

*If the iPad or iPhone has a Lightning port, you need to use Apple's Lighting to USB3 camera adapter with an external power supply.

How to use Apogee Groove with iPhone or iPad

This is because Groove is a high-performance headphone amplifier and DAC designed to power the most demanding premium headphones. Though the newer USB-C iPads are able to supply enough power, Lightning-only iOS devices do not provide enough power for high-quality headphone drivers without this adapter.