Actually, that's not accurate.
ANY motherboard with a "Ryzen 3000 ready" sticker on the box will have already been updated to a compatible BIOS version for Ryzen 3000 series CPUs and will be GUARANTEED to work with them. Any motherboard that doesn't have one, and isn't a "Max" model, won't be guaranteed and will be a crapshoot as to whether it has BIOS support or not. It's LIKELY however that if there isn't a sticker on the box, then it has not been updated and won't be compatible. The only way to know that for certain is to buy at a local retailer and LOOK at the box, or ask the online retailer via phone or online chat, but in that instance as I said you may or may not get accurate information.
You can also reach out to specific motherboard manufacturers who would be the MOST able to direct you to retailers that are for sure selling versions of those boards that are compatible and have the required BIOS version.
Or, you could simply get a B550 motherboard since today was the release date for those to start being sold. What actual availability looks like, well, guess we'll have to see. So far, those all seem to have availability dates that are anywhere from a few days to a couple of weeks further out, or show as out of stock, on Newegg. Amazon doesn't even show any right now. Other vendors,