We’ve seen some B550Ax motherboards a while back, but those weren’t the real deal. Instead, they were just B450 refreshes for OEMs. Now Videocardz has shared the first image of a B550 board which supports PCIe 4.0 across all slots and connectors. Back in July, when the X570 first hit the market and the BIOS updates started rolling out, many B450 boards did support PCIe 4.0 despite AMD deciding against it. Of course, that changed soon as Team Red launched a slew of AGESA updates, disabling the feature on other motherboards.
Update:

So turns out there’ll be a B550 and A520 chipset. While the former will support PCIe 4 across the discrete PCIe x16 and NVMe lanes, but the rest of the GPL and chipset uplink lanes will continue to use PCIe 3. This is because the B550 chipset doesn’t support PCIe Gen 4.0 natively. However, AMD allows motherboards to access PCIe Gen 4.0 protocol from the CPUs.
A520 is a lower-end part and won’t support either the PCIe 4 standard or overclocking. It mainly upgrades the General Purpose Lanes to PCIe Gen 3 and supports USB 3.1 Gen 2. Other than that, it’s mostly identical to the B450 chipset.

The initial B550A boards were actually just B450 parts with PCIe 4.0 support on the primary x16 slot while the rest ran at standard 3.0 speeds. The new B550 boards are expected to support PCIe 4 across all slots. The board Videocardz has shared is from SOYO, a Chinese company that manufactures Maxsun products. It’s a micro-ATX motherboard with two PCIe slots and dual-memory DIMMs. The SOYO board seems to have a 4+2 VRM with two MOSFETs instead of one per phase. I’m not certain whether this has any actual benefits and if it’s utilizing doublers, but the latter is unlikely.
The board has a dragon graphic with the SOYO name in between. This is eerily similar to MSI’s logo. We’ll keep you posted if we catch wind of any more B550 boards.