Well this is interesting. I plugged my phone into my computer to pull some photos off of it and I just happen to start browsing it via Windows Explorer since the device shows up there. Imagine my surprise when I saw things that were in my Hidden folder show up clear as day. It seems that lock is only at an application level and just browsing the file system it’s there to see.
Does anyone else experience something similar? Is there a note I missed that it’s still be available via other means?
The device shows up there because you connected to your computer and trusted the connection on your iPhone (and you had to type in your passcode to confirm.) If someone doesn't know your passcode they can't do this. If they do know it, they could access your photos anyway.
It's probably worth filing a Feedback report to request Hidden photos don't get served up over the standard file system access alongside the rest of your library. You can do so by typing applefeedback:// into Safari and hitting return. If you're on a developer or public beta, you can simply use the Feedback app instead.
That makes sense but the one difference I see is the hidden/deleted folders are Face ID locked and you need to be present to access them at the time. Just having the passcode can get you in to the phone but not to those folders, yet all you need is the passcode for file system access.
As an added layer of security, you can set the phone to self-destruct by going to Settings > FaceID & Passcode > Erase Data. If someone enters the incorrect passcode more than 10 times, the phone will erase itself. Assuming a 6 digit passcode, there are 1 million possible combinations. An attacker would have an effective 1 in 100,000 chance (.001%) of guessing your passcode correctly