https://arstechnica.com/gadgets/2022/03/speedy-new-5800x3d-is-amds-first-non-overclockable-ryzen-processor/

AMD's Ryzen 7 5800X3D promises to be one of the company's fastest gaming CPUs, and it's one of the last high-end chips that will grace the AM4 socket before Ryzen 7000 CPUs come out later this year. But its experimental new 3D V-Cache stacking technology comes with one negative side effect: This will be the first Ryzen CPU that's incapable of overclocking.

According to PCWorld, AMD Marketing Director Robert Hallock says that this is because the processor's voltage limit is locked to 1.35 volts, a bit lower than other Ryzen 5000 chips. A lower voltage for the CPU cores means they'll generate less heat, presumably creating a bit more thermal headroom for the 64MB of additional L3 cache memory that the 5800X3D uses. It would also explain why the 5800X3D's clock speeds are a hair lower than the standard Ryzen 7 5800X.