In a nutshell: Samsung is experimenting with a new feature in South Korea called "repair mode." As the name suggests, it's a special setting that you can toggle on when you take your phone in for repairs that protects your data from nosy repair technicians.
Now that Samsung has pointed it out, it sounds strange to say that we hand over our phones, with all their sensitive data onboard, to repair shops with the password on a slip of paper. Many minor repairs don't require the phone to be unlocked, but those that do present a significant security risk if you have important information on your phone, particularly if you use it for work.
There have been many documented instances of repair technicians misusing their access to customers' phones (or PCs before that) and getting caught. In 2016, two employees at Pegatron, one of Apple's major repair contractors, found explicit images of a college student on her phone and posted them on her Facebook account. She sued Apple for $5 million and settled privately for a multi-million dollar sum, which was eventually paid for by Pegatron. Apple conducted an "exhaustive investigation" afterward.
Samsung's repair mode is meant to prevent similar situations from happening. In the mode, the phone becomes a blank canvas: your photos, messages, and accounts all disappear and only the default apps remain visible. It lets technicians try all the normal phone functions, like taking a photo to see if the camera has been repaired successfully, but keeps them contained in an isolated environment. Ars Technica speculates that the mode works by creating a new, temporary user account within a different drive partition.
Samsung says repair mode will be added on an upcoming update for the South Korean version of the S21 series, with more devices to follow. When the feature arrives, you'll be able to find it in Settings > Battery and Device Care > Repair Mode. This will restart the phone and take you to the blank account, which doesn't require a password. To disable it, you simply restart your phone again, unlock it the usual way, and it'll be back to normal.
Given how useful it sounds, we'd like to see a repair mode become a standard feature on more devices. It could conceivably become a default Android feature, but before that can happen, Samsung needs to finish testing and release it to the public for the newer S22 series as well as internationally. No word on when that will be, but hopefully in the not-too-distant future.
Image credit: Shri