Hi,
Looks like this is a developer issue not Appium issue. In my application too have date selection and its working fine.
Ask the dev team to make element as "XCUIElementTypePickerWheel" and sendKeys or setValues method will work.
//code:
@iOSFindBy(className = "XCUIElementTypePickerWheel")
private List iosDatePickerWheel;
iosDatePickerWheel.sendKeys(keys)
iosDatePickerWheel.setValue(keys)
Regards
Blogger