If you want to lock an app on One UI, your options are very limited. You move it to the Secure Folder, a safe enclave that's locked with your verification method of choice and keeps the data entirely separate from the rest of the device.
However, if you don't want to use Secure Folder, you're basically out of luck. That could change, if the team working on the One UI 7.0 beta program take up the suggestion, especially since individual locking of app outside the Secure Folder is already possible on One UI in China.
China already has this feature on One UI
There are many scenarios in which having the ability to lock individual apps would be a good feature to have. For example, if your kids watch YouTube on your phone, you can keep sensitive apps locked and then rest easy when they run off with the device. Perhaps it's a shared device and you'd prefer the additional privacy, either way, locking apps would be super helpful.
You can hide apps away in the Secure Folder but then that limits your ability. Nothing outside the Secure Folder interacts with things inside it. You have to manually shift content, files, and more from there, which makes for a less desirable user experience on a daily basis.
People have been asking Samsung on its official forums to consider an app locking feature for One UI 7.0. They've also pointed out that One UI already provides this for users in China, a minor market for Samsung, so it's only right this feature is extended to its most important markets.
A member of the One UI beta team has responded, highlighting that the suggestion is currently being evaluated by the project manager. If it's found to be in alignment with Samsung's design concept and goals, the One UI 7.0 team will consider releasing this feature with the public version of this update.
So this is all pretty much up in the air at this point in time, but at least the suggestion has been acknowledged and one would hope that it eventually does end up being a feature on Samsung's mobile devices.
