How secure are photos in the secure folder?

I've recently moved some private photos off my gallery and into my secure folder on my Samsung S22 Ultra. However, I've noticed that despite these images being completely wiped from every other spot on my device, including cloud storage, one app - which has no extra permissions other than basic gallery permissions - can still access them. It's an icon changing app (Icon Changer - App Icons by Eco Mobile Style) where you can use your own photo as a thumbnail for an app (it creates a second home screen icon.)

Is this a major security concern I should be worried about with this app? It certainly feels very creepy that it can casually access photos that should be locked. It can't even find most albums on my normal gallery.