If the motherboard is REAL (As in ACTUALLY factory updated), purchased through a valid partnered site like directly from Amazon, Newegg, etc., not through a 3rd party seller that might slap a fake sticker on the box and sell you an older production model of the same board that hasn't been given updated firmware, then if it has that sticker on the box it WILL have the latest firmware and WILL be ready to install the 2nd gen Ryzen 2000 series CPUs.
Doesn't matter what brand it is.
At this late date, I wouldn't worry at all since pretty much any old stock should be gone and all the boards should come with new enough bios to support those chips. Honestly however, I would not recommend the B350 motherboards to anybody building a system right now. Even with the latest BIOS updates they do not have as good of memory compatibility and support as the B450 or X470 boards. Unless you absolutely HAVE to go with B350 due to cost, I'd really try for at least a B450 chipset.
If you plan to run an overclocked system, I'd further recommend that you stick to X470.