I think you can take the Bazooka off your list, the Mortar just seems better.
The B550-A PRO is ATX which can be nice.
My vote would be for the Mortar. It seems the best spec, and gives you a bit of flexibility should you want to change cases at some point to something smaller. I say a bit, it wouldn't fit well in my wife's matx case as the sata ports mostly point horizontally which would go straight into a wall of metal, but it looks like two are usable which would be enough for her old hard drive and DVD drive (with C: being on NVMe). So get that board, just don't get a Silverstone shoebox style case for it
PCIe is very good for compatibility, I would be utterly stunned if your GPU didn't work.