https://gamersnexus.net/guides/3582-amd-chipset-differences-b550-vs-x570-b450-x470-zen-3
It's Steve Burke, so a little wordy but this article outlines the differences between X570 and B550. Basically B550 only supports PCIe 4.0 on the CPU, and PCIe 3.0 on the chipset and the link between the two is PCIe3.0. The X570 has native PCIe 4.0 on the chipset, and the link between the chipset and CPU is PCIe 4.0. What does this mean to you? B550 = 1 PCIe gen 4.0 NVMe slot (linked to CPU) and 1 PCIe gen 3 NVMe slot (Chipset), X570 = 2 PCIe gen 4.0 NVMe (CPU, Chipset respectively) slots. There are other differences of course, but that is what you will notice right off the bat. I encourage you to suffer Steve Burke to learn the rest and decide if it applies to your use case. I decided that for me, it did not. Storage transfer rates have well outpaced the demand, even a SATA 3 SSD will suffice and most people will never even notice the difference, even under the most demanding tasks.