Busybox upgrade to newer(v1.21.1)

Hi all,
My WD runs on v1.20 and I’d like to upgrade it to a newer version. I checked v1.21.1 and looks like it works. however after reboot it goes back to the original version.

is this is something can be change? or it’s hardcoded to this busybox?

Thanks.

shame that WD still working on such an old limited busybox :frowning: