A small number of DDR5 systems and motherboards require a period of "training" newly installed memory to work with the system and allow access to the UEFI, or otherwise to complete the system's power-on self-test (POST).
www.crucial.com
Intel boot isn't instant (no UEFI boot will ever be
), but afaik, Intel either doesn't need this or it just does it much, much faster.
The worst part is there's no feedback during this process, so users may unknowingly reboot, restarting the whole process and wondering why there's no more POST anymore.