Why isn't my RAM running at its advertised speeds?

Your RAM defaults to safe, slow JEDEC speeds (2133MHz for DDR4 or 4800MHz for DDR5) until you enable XMP (Intel) or DOCP (AMD) in the BIOS. Restart, mash Del or F2, find the XMP/DOCP setting under the overclocking or advanced memory tab, enable it, save, and exit. If it fails, clear the CMOS and try again.