You could solve this a number of different ways, here are some suggestions:
You could also use custom validation on the input fields:
This way, when the checkbox is not checked, the validation will be true, and otherwise it will check that the input field is not empty
EDIT: I now see that you are using modeler 6.10.4. So my solution is unfortunately not usable for you. Maybe a good reason to migrate to Mx7 ;-)
Remove the required field validation and write your own in a microflow. In the microflow you can put an exclusive split which looks if the check box is checked, if it is do a check if the required attribute is empty or not.