Mobos
Mobos
PCIe 4 compatibility isn't necessary for your setup. You can use a board like the A520, which offers similar power delivery to the B550 but is more affordable and suitable for your needs since you're new to overclocking.
PCIe gen 4 isn't essential unless you're after high-speed storage. You probably won't feel any change compared to gen 3. I wouldn't choose an A520 board. You'd save roughly $30 to $40 by skipping the B550, and those missing features aren't worth that much.