I'm working on an app using Flutter that is being rolled out on both Android and iOS. Some iOS users have expressed confusion at the 'ripple' effect that appears on a surface when it is tapped or pressed. Is this an uncommon interface feature on iOS and if so, is there a more common behaviour when a surface is touched?
The default behavior for buttons in the Apple HIG doesn't include a ripple effect. You can check out the HIG guidelines for buttons here, which don't specify any particular behavior. However, it's possible to create a variety of effects using Swift, Cocoa, Flutter, and other tools. As you've already done, you can create a ripple effect if you like.
Whether the ripple effect is confusing or simply unexpected is a different matter. It's possible that users might find the unexpected effect appealing, so when conducting user testing, it's important to ask users if they're bothered by the feature or if they like the aesthetic. It's worth noting that Android users didn't always have this feature, but they seem to have adapted to it without issue.