“To that extent” in this context means that the remainder of the contract stays valid. The interpretation you state is not only incorrect, it would be toothless to introduce it because people could simply work around it by adding that clause and arguing that it constitutes a sufficient exception under the law.
As for why the “to the extent” phrasing exists, consider an example: an employment contract consists of two clauses, A: that prevents the employee from disclosing confidential customer data to third parties, and B: a non-compete clause (which does come under the same provision mentioned by grandparent). If the employer ever sues an employee for violation of A, they shouldn’t be allowed to argue that they aren’t subject to it because of clause B.
As for why the “to the extent” phrasing exists, consider an example: an employment contract consists of two clauses, A: that prevents the employee from disclosing confidential customer data to third parties, and B: a non-compete clause (which does come under the same provision mentioned by grandparent). If the employer ever sues an employee for violation of A, they shouldn’t be allowed to argue that they aren’t subject to it because of clause B.