ASMedia has reportedly landed orders to make AMD B550 and A520 chipsets for the Ryzen 3000 platform and will be supplying the same to motherboard OEMs by Q4 2019. These chipsets will continue to be based on PCIe 3.0 as PCIe 4.0 is currently exclusive to the AMD X570 platform. ASMedia is expected to tape-out PCIe Gen 4 designs by end of this year and will offer AMD chipsets with PCIe 4.0 support some time in 2020.
https://www.notebookcheck.net/ASMedia-to-produce-AMD-B550-and-A520-chipsets-based-on-PCIe-3-0-PCIe-4-0-only-in-2020.424009.0.html