Found out by chance:
You have to be root, that is log with root account or type "su -" (not "su"), nor "sudo armbian-config".
I'm a noob, I recently found out in plain x86 Debian that "su" is not equal to "su -".
I think, tell me if I'm wrong, that's something recent in Debian world. It didn't use to be like that. Should it be pointed out somewhere? It can be misleading to newbies.