This seems to be a tool aimed at employers, enabling them to compare and verify salary data of potential candidates. It adds to the information imbalance already present and doesn't seem to be empowering or helping employees unless they actively share their numbers - an option they always had.
No, they didn't. Many contracts explicitly forbid it and not every employee has the knowledge, courage or frankly financial stability to go against their employer.
In fact, most of them openely discuss such matters.
Never got why in US it is so "pssst, keep it low" when discussing such matters.