you can remove tap animation by setting spash & highlight color to transparent
MaterialButton( splashColor: Colors.transparent, highlightColor: Colors.transparent, enableFeedback: false, onPressed: null, ),
check for the condition if the bool value is true if you will pass null so your onPressed will be null and RaisedButton will be disabled, you can also provide the disabled color.
onPressed: trueCondition?(){trueCondition = !trueCondition; }: null