I think that "SB" is good enough here, the option name shows the unabbreviated
name.
" --qemu-mem=MEM Configure guest's RAM size\n"
" --qemu-kvm= Configure whether to use KVM or not\n"
" --qemu-gui Start QEMU in graphical mode\n"
- " --secure-boot= Configure whether to search for firmware which supports Secure Boot\n\n"
+ " --secure-boot= Configure searching for firmware with SB support\n\n"
"%3$sCredentials:%4$s\n"
" --set-credential=ID:VALUE\n"
" Pass a credential with literal value to container.\n"