SwiftUI : returnKeyType

Could you explain how you would need to use this "equivalent" ?

I would simply like a "Done" button on the keyboard.

It depends on the keyboard. Which keyboard type do you use (Decimal, ASCII, default…)

Found this thread to explain clearly how to set keyboard type (some include a done key) in SwiftUI.

https://stackoverflow.com/questions/56517515/how-to-set-keyboard-type-of-textfield-in-swiftui

It's default.

TextField("Leave a comment", text: $comment, onEditingChanged: { if $0 { self.kGuardian.showField = 0 } }) {
                commentText = self.comment
            }
               
                .padding()
                .background(GeometryGetter(rect: $kGuardian.rects[0]))
                .background(Color(red: 239.0/255.0, green: 243.0/255.0, blue: 244.0/255.0, opacity: 1.0), cornerRadius: 10.0)

As of iOS 15, you can use .submitLabel(.done) to set the done button on the keyboard. Documentation is here: https://developer.apple.com/documentation/swiftui/view/submitlabel(_:)