It seems ASRock is adding support for AMD’s Zen 3 based processors to at least some of their X370 motherboards. The first board to get support is the X370 Pro4, which is a pretty standard board, nothing too exciting about it. Maybe they decided to go with this board to test if it is worth adding support for Zen 3 support across all of their X370 motherboards.
Support has been added support for AMD Vermeer-based CPUs (Ryzen 5000 series) and well as several Renior-based APUs. The new P7.10 UEFI update is required to support these CPUs and it also drops support for the rather old Excavator+ based Bristol Ridge APUs. It will be interesting to see if ASRock adds this support across all of their X370 motherboards and if other motherboard makers follow suit.