As a very belated reply, the main difference between B550 and x570 is that the chipset itself supports PCIe4. Ryzen 5000s do 20 lanes of PCIe4 natively, so slots connected to it will be PCIe4 automatically. Typically, this is two slots and an M.2 port. 4 lanes go to the M2, and the other 16 either go all to one slot, or are split into x8 and x8.
From there, any additional M.2 or PCIe slots on B550 will be PCIe3. On x570, they’ll be PCIe4. Most x570s also come with more USB ports. (I believe mine has like 13 USB ports on the back, plus a few more connectors for the front panel.)
It’s not really a major difference, and the easier cooling on the 550 can be nice. If your case is airflow-constrained, a B550 might be a superior solution.