Terms of use are not legally binding in case they contain something that contradicts the existing law, just like any other contracts.

For example, imagine an employer wrote an employment contract signed by all employees that said something obviously against the law, like "if you get pregnant, we are letting you go". Even though employees signed this contract, that specific clause was against the law, so there is no way to legally enforce it. If the employer tries to legally enforce it, they will be in for a rude awakening.

Another, more realistic, example. Let's say you are about to get married and decide to get a pre-nup. Both you and your partner sign it. Let's say both signed a clause that says "any future earnings made during this marriage will get split 90/10 in case of the divorce, not as a 50/50 split". If divorce actually happens, this clause will be entirely useless, despite both parties willingly signing it. Both of the people who signed it will be able to claim total 50/50 on the split, even if they initially agreed to a different split.

tl;dr: the law overrides anything one can put into their terms of use or any other contract.