I don't know if there is an option to disable ipv6 on bootloader level but that's not necessary anyway. You can do that in userspace via sysctl.conf, just use your favorite search engine and you will find how this works.

Without any research I assume this firmware package contains some fw files that are just there in case somebody wants to reflash some otherwise inaccessible fw storage. Similar to u-boot packages which on upgrade will store the necessary binaries for reflash on fs but does not actually reflash itself in the boot sector. Needs to be done manually. So tl;dr: having this optional makes sense.

https://zuckerbude.org/armbian-using-kernel-config/ Once successful tested provide a PR to add the missing module:https://docs.armbian.com/Process_Contribute/

Would like to be running fail2ban but missing an important kernel module -> xt_multiport Any ideas on obtaining this? modprobe: FATAL: Module xt_multiport not found in directory /lib/modules/6.12.22-current-rockchip64

that should be 1500000 (one more zero). Note a lot of uart connectors can't handle this high of a speed. There are many threads in the forums discussing specific ones that are able to reach that speed.