As was the case with the move to DDR4 memory with Skylake and the move to DDR3 with Core 2-series processors, Intel’s first DDR5-enabled platform is also backward-compatible with DDR4 SDRAM. That means that we’ll be seeing motherboards for Intel’s Alder Lake-series processors that accept DDR4 memory instead of DDR5 memory—and possibly boards

Source: Hot Hardware – Renders Showcase ASUS Prime Z690 For Alder Lake With DDR5 And DDR4 RAM Support