As Ralph mentioned, electromagnetic catapults are a proven technology.

An interesting article:
Full steam in reverse: Trump orders US Navy back to old-style aircraft catapults

Some quotes:
"There was once a substantial technical case against EMALS, whose problems caused significant delays to the completion of USS Ford and her entry into service. Unfortunately for the President, the technology has since matured, and the argument for a return to steam is about a decade out of date."

"Whatever criticism can be made of the tortuous development history, its electromagnetic launch system has now demonstrated its maturity."

"The decision is particularly difficult to reconcile with the memorandum’s own diagnosis of what has gone wrong with American shipbuilding. It explicitly criticises “iterative design change procedures” for causing cost growth and delays, yet only a few paragraphs later it orders one of the most profound late design changes imaginable to a 100,000-tonne nuclear-powered warship."

"The change is not analogous to fitting a different radar or weapon to a ship. It means redesigning substantial parts of a complex nuclear-powered aircraft carrier whose detailed design has already been completed. General Atomics says its work on the EMALS and AAG equipment for Doris Miller is already nearly 50% complete. Abandoning it would write off work already paid for, before the cost of designing, manufacturing and integrating a replacement had even been considered.

Estimates remain speculative until the USN completes the study Trump has ordered, but the bill could run into billions of dollars. The greater damage may be to the schedule. Doris Miller is not due in service until the 2030s, and delaying another carrier is the opposite of what a memorandum intended to accelerate US naval shipbuilding should achieve."