I had the exact same problem with the same components: New PC build with Ryzen 9 5900x, Crosshair VIII Dark Hero, Corsair Vengence LPX 64GB DDR4 3200MHz, RTX 4070 Ti. No matter what I did, all cores were locked at 547 MHz. The UEFI was correctly set with DOCP and registered the CPU at 3900 MHz, the DDR4 was set to 3200 MHz -- everything looked right. But CPU-Z registered the cores at 547 MHz???? Cinebench 24 multicores was giving showing s a dismal 133 pts, which should have been ~ 1200. I was really stumped -- for weeks, I'm embarrassed to say. But the problem was a SIMPLE FIX -- the Slow Mode switch on the MB was enabled, which should be disabled. I disabled this switch and the CPU cores jumped up to 3900 MHz. Somehow during the install I must have inadvertently engage this switch without knowning it. I didn't even know this switch existed, which FYI, is used when an overclocked CPU becomes unstable and causes the system to crash. If that happens, you enable this switch and the CPU runs at reduced freq (547 MHz in this case) so you can adjust parameters. The PC still runs fine at 547 MHz, just at 1980s PC speeds. Hope this helps someone --- it was hardcore misery for me for weeks, I'm embarrassed to say. Although, the upside when you expereince something like this is I really learned alot more about parameters tweakings in the UEFI (voltage settings, etc) CPU optimizations, GPUs, and motherboards.
