I have newly bought a Strix Flare 2 from my Strix Flare 1
I can control the brighness using Armoury Crate and keyboard FN shortcuts when I am using basic light affects, but when I change the light to Aura Sync use the profile built in Aura Creator (or make a new profile), I can't control the brightness at all, even no any options to change in Aura Creator, either the keyboard FN shortcuts
I don't use Aura Creator much, so I'm not too familiar with it but...
Aura Sync is to sync all my devices (including ARGB/RGB headers) with the motherboard lighting. The Aura effect changes the motherboard lighting and all my devices change with it.
So, when you have your keyboard synced in Aura Sync, it should be using the Aura Effects profile in Armoury Crate.