I previously owned a Samsung, and got confused by the Fort Knox feature. The description of the feature said that only I could access it, but required me to sign up for an Samsung account to use it. I never understood why I needed an online account to use an offline feature, and it also said I needed to register in case I forgot the password and would need to regain access.

I was determined not to have a Samsung account to use the phone, so I never got try it out, but I assume that anyone with access to the Samsung account have access to the secure folder