I want to limit input on textfield...

You shoals use the onChange on TextField to test on the fly. Do it in onSubmit to test only when you hit return key.

If the State var in the TextField is input, you should test if only letters

                    .onChange(of: input) { oldInput, proposedInput in
                        if onlyLetters(proposedInput) {
                            input = proposedInput
                        } else {
                            input = oldInput
                        }
                    }

onlyLetters is a func to test the proposed string contains only letters.

func onlyLetters(_ s: String) -> Bool {
  return resultoftest
}

See here a way to implement: https://stackoverflow.com/questions/60657152/how-to-check-whether-string-only-consists-of-letters-and-spaces-in-swift-5