Since One UI 8 beta 1, I had an issue where the I couldn't change the icon for the Secure Folder for the icon pack I was using. It would show the default Samsung icon, though I could go into the Secure Folder and customize the icon that way. Now I think I finally found out to change the icon to something from the icon pack I'm using (Outlines).
In Theme Park, create or edit you icons like you normally would. Tap the "3 squares and a +" icon at the top right to manually change the Secure Folder icon and apply the icon pack. Then go to the Secure Folder and tap Reset, then Save. That should change it to the your icon but if you had changed the name,it will reset that back to "Secure Folder". If you want to rename it, you may have to tap Reset, change the name, then hit Save. But that should do it.
Hope this helps anyone else that was having this issue!
