Do not delay making updates to the state: When you callonValueChange, update your TextField synchronously and immediately:

class SignUpViewModel(private val userRepository: UserRepository) : ViewModel() {
   fun updateUsername(input: String) {
        viewModelScope.launch {
            // async operation
            val isUsernameAvailable = userRepository.isUsernameAvailable(input)
            // ...
            if (!isUsernameAvailable) {
                // modify error state
            }
           username.value = input
       }
   }
}

viewModelScope

Dispatchers.Main.immediate

isUsernameAvailable

isUsernameAvailable

username.value

Dispatchers.main.immediate

synchronously and immediately

TextField