OnePlus is in the midst of preparing its Android Q release, but that's not stopping progress on its existing apps and services. Recently, we saw the Gallery pick up a new carousel interface for Collections, and today, another update to the app lets you hide your photos from the main view, though you shouldn't rely on it to avoid prying eyes.
You'll find the new Hide button under the overflow menu for each photo or video, or if you multiple select several items.
Left: OnePlus Gallery 3.3.10. Right: OnePlus Gallery 3.4.4.
Once you hide a media file, it will only be viewable from the Hidden Collection, which is easily accessible from the overflow menu on the top right of the app. OnePlus doesn't require a pin code or fingerprint to open this collection, so there's no real protection or security measure to ensure someone wouldn't snoop in and see those images and videos.
Accessing your hidden photos and videos.
That's why you're better off using this more like an archiving option to remove receipts and documents (for example) from your main gallery, or only if you trust that no one will snoop in there and discover some things they shouldn't see.
If you want to try out this feature, you need to have OnePlus Gallery 3.4.4, which is available on APK Mirror.