Adding my NAS Drive to Safe Files

I've just acquired and installed Bitdefender Internet Security 2020 and am in the process of configuring it.

However, I cannot find a way to add my NAS drive folders to my Safe Files. As my NAS drive is my primary storage space, I need these protected against attack from ransomeware, etc.

Bitdefender only shows me the folders on my computer's hard drive when I try to 'Protect more folders'.

Any ideas please?