It must be noted that while the new upcoming chipset might be called B550, this particular motherboard looks to be a B550A board,
which are OEM boards as confirmed by AMD in October last year. In fact, this is the same motherboard as was spotted in October.
AMD's Robert Hallock to be a rehash of the B450 chipsets but for OEMs, only featuring PCI-Express 3.0. The specifications we found now, however, point to the motherboard having PCI-Express 4.0 on all fronts. Therefore, it's possible there may be only one B550 chipset, and that the "B550A is for OEMs" argument was meant to throw the community off.
PCI-Express 4.0 was rumored, but not certain, to arrive on the B-series platform. The PCI-Express 4.0 support isn't quite as extensive as on the X570 motherboards, though it's unlikely to affect customers interested in these boards.
Whereas the X570 motherboards have PCI-Express switching that brings PCI-Express 4.0 lanes to all the PCI-E slots, and can split them across multiple slots if necessary, the B550AM Gaming from ASRock only delivers PCI-Express 4.0 support on the uppermost slot and to the M.2 slot. The second PCI-Express slot might look like an x16 slot, but on this Micro-ATX motherboard will only fuel four lanes of PCI-Express 3.0 via the chipset. Wiring the PCI-Express slots straight to the CPU is a cost-saving measure, but a perfectly acceptable one on a B-series board. After all, most people don't use more than one graphics card, so chances are that these limitations won't affect many. Those who do need more options can opt for the X570 or better motherboards.