Ok, well this may be more over my head than what I'm capable of understanding. I'll need to research what the right BIOS is then to be able to confidently buy this combination.
Easiest thing to do is to read reviews and/or find someone who owns the board and has tried a Matisse chip in it. Some people lost the ability to use the mouse in the UEFI screen (for example). We have at least one forum user here -
@VirtualLarry - who I think has a B450 with an R5 3600 in it, and of course
@Markfw can tell you about Matisse in some x370 and x470 boards (mostly ASRock ones). Here is one of the major issues you're looking at with B450:
MSI is among the motherboard manufacturers who had to significantly modify their UEFI firmware packages to cram in AGESA ComboAM4 1.0.0.3ab microcode on their AMD 300-series and 400-series chipset motherboards, due to firmware ROM size limitations. Most older MSI AM4 motherboards have 128 Mbit...
www.techpowerup.com
MSI Max boards actually have 32MB firmware chips to circumvent this problem. I would look at some of those and see if they meet your needs and your budget. Examples:
(look for the ones with "MAX" on the end)
If you want something better than B450 . . . I would start looking at old x370 and x470 boards first, to see if there's something there you like. x570 is only really good for PCIe 4.0 support or, in some extreme cases, insanely good VRM setups that you won't need anyway.