Bios files are installed in the bios chip on new boards by the factory after a release. So with prior gen releases and newer bought boards it's iffy. All B450 motherboards manufactured shortly after the release of the 3000 cpus should be 3000 cpu compatible. But there's no saying as to whether you get a newer board from a vendor, one that's been sitting in customs for 6 months, one from a shop that ordered 10 a year ago and this is the last of that batch.
Iffy.
The MAX boards were not released until after 3000 series, so include a 3000 rdy bios, there isn't any choice, that's how msi planned it, markets it, brags about it. There's no confusion. If it's a MAX, it's good for 3000 cpus.