Many vessels in history have had two or more methods of propulsion.
Galleys have both sails and oars.
Most 19th century steamships had both steam engines and masts and sails. most large modern sailboats have both sails and motors.
The Great Eastern (1858-1889) had two side paddle wheels and four steam engines for the paddle wheels and another steam engine for the propeller. It also had six masts and a large amount of sails.
Many later vessels have multiple steam engines and multiple propellers. Many modern ships have multiple propellers in pods attached to the, ship and the pods can be turned in various directions for flexibility in maneuvering.
Many large aircraft carriers of today have one or more fission reactors to power their engines, even though they are smaller than your super carrier.
Therefore, I deduce that your super carrier would have hollow areas inside its unsinkable block structure, containing enough fission reactors - or possibly fusion reactors if far enough in the future - to power the ship.
For propulsion the atomic reactors would generate electricity and the electricity would be transmitted by wires to many propellers in many pods attached to the main hull of the super carrier.
For reasons of stability the massive nuclear generators in their hollow areas should be placed rather low in the ship. So they might be partially below the waterline, and thus could possibly flood with water.
To counteract that the super carrier should contain water storage tanks containing an equal mass of water as would fill the hollow areas containing the atomic reactors. If the atomic reactor areas start to flood, water can be pumped from the storage tanks into the sea to maintain the weight of the super carrier at a constant level, while pumps also pump water out of the reactor areas.
You may remember Tom Clancy's 1984 novel The Hunt for Red October and the 1990 movie based on in. The Soviet submarine Red October is supposedly equipped with a stealthy magnetohydrodynamic (MHD) dive to use only magnets, with no moving parts, to travel though the water.
MHD has been studied for propulsion of surface ships, submarines, aircraft, etc.
MHD has no moving parts, which means that a good design might be silent, reliable, and efficient. Additionally, the MHD design eliminates many of the wear and friction pieces of the drivetrain with a directly driven propeller by an engine. Problems with current technologies include expense and slow speed compared to a propeller driven by an engine. The extra expense is from the large generator that must be driven by an engine. Such a large generator is not required when an engine directly drives a propeller.
The first prototype, a 3-meter (10-feet) long submarine called EMS-1, was designed and tested in 1966 by Stewart Way, a professor of mechanical engineering at the University of California, Santa Barbara. Way, on leave from his job at Westinghouse Electric, assigned his senior year undergraduate students to build the operational unit. This MHD submarine operated on batteries delivering power to electrodes and electromagnets, which produced a magnetic field of 0.015 tesla. The cruise speed was about 0.4 meter per second (15 inches per second) during the test in the bay of Santa Barbara, California, in accordance with theoretical predictions.
Later, a Japanese prototype, the 3.6-meter long "ST-500", achieved speeds of up to 0.6 m/s in 1979.
In 1991, the world's first full-size prototype Yamato 1 was completed in Japan after 6 years of R&D by the Ship & Ocean Foundation (later known as the Ocean Policy Research Foundation). The ship successfully carried a crew of ten plus passengers at speeds of up to 15 km/h (8.1 kn) in Kobe Harbour in June 1992.
Small-scale ship models were later built and studied extensively in the laboratory, leading to successful comparisons between the measurements and the theoretical prediction of ship terminal speeds.
Military research about underwater MHD propulsion included high-speed torpedoes, remotely operated underwater vehicles (ROV), autonomous underwater vehicles (AUV), up to larger ones such as submarines.
So depending on how advanced the society of your story is, the super carrier might use a MHD drive full time or part time.