"force allow apps on external" on EMUI 5.x not toggling on so i've been trying to force allow apps on external storage by ticking the option: force allow apps on external
 under the developer options segment of the phone but it just doesn't seem to work. Every time I try to  toggle this setting on, it just refuses to turn on it goes back to its original greyed out state. 
Please note that I have set my Default Storage" to SD; Could this be the reason ?

Thank You,
Wael
Huawei has disabled this function. It won't work unless you root the device.

Source: Huawei support website.