I'm having this exact same problem with an S10 on AT&T.
I set up the secure folder and the Samsung Gallery app was there. I'm not sure if there's any way to move the app out of the secure folder, but the phone doesn't seem to be detecting that the app is installed from the default camera. I get an error that says "Unable to find application to perform this action" whenever I try to view a picture that I just took. The version of Samsung Gallery available on the Play Store seems to be different (the icon I can see in the secure folder is a red flower; the one on the Play Store is yellow). The one on the Play Store is also apparently not compatible with my device.
Really a ridiculous problem to have right out of the box. I hope you figure out a solution to this soon.
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