ASUS is Working on a DDR4 RAM Adapter for DDR5 Motherboards
That said, considering that a lot of high-end Z690 motherboards only support DDR5, this might be an interim solution that makes sense for a lot of people until availability of DDR5 improves. There’s some complexity in making the adapter work though, as not only does it need its own power regulation, since DDR4 memory doesn’t have onboard power conversion components unlike DDR5, but there’s also the 2x 32-bit vs 64-bit bus to take into consideration as well. On top of this, the DRAM traces are obviously extended, which could lead to instabilities, which is why it’s apparently only tested with one type of memory right now, which appears to be G-Skill’s Tridentz Royal. A further limitation of the adapter is that it requires a special UEFI version to be installed that allows DDR4 memory to be used, but this might be the smallest issue in this “skunk works” project from ASUS’ ROG team.