For my https://eu-os.eu project, I switched to AlmaLinux packages. They build by default for arch = amd64v3. On old hardware (think of schools), this does not run anylonger. Also not on my Thinkpad x220 test device. A PR is open to build the bootc image for amd64v2 as well. https://github.com/AlmaLinux/atomic-desktop/pull/38
It seems to me that bluebuild does not expose the --arch flag from podman, so I do not see how I could force bluebuild to pick one x86_64 over the other (unless I build on a device with only v2 support).