Likely a bios update you need to apply. At one point the B450s weren't going to support Zen 3. AMD reversed course later, but that likely means that a bios update had to come along in order to add the support.
Lots of motherboards, even new ones, still ship with old-ass bios.
Also, remember that memory-training is a thing now -- don't assume that 10 seconds of a black screen means it won't post. Easily wait a minute or more - board could just be in memory-training to get the best speeds.
I usually physically take drives out and boot without them before wiping. Just something I do now, because of this exact situation.