Ryzen 4500 and Ryzen 5500 only support PCIe 3.0 as well.
The RX 6600 only uses PCIe 4.0 X8 so there could be performance loss if only in PCIe 3.0 mode.
The requirements I have read say you can run SAM in both PCIe 3.0 and 4.0.
Ryzen 7 7800X3D, ASUS ROG STRIX X670E-F GAMING WIF, G.SKILL TRIDENT Z NEO 2x16GB DDR5 DRAM 6000MT/s CL30, AMD Radeon RX 7900 XTX, LIAN LI EDGE 1300, Corsair MP600 PRO NH 4TB