A new update is now heading out to the Samsung Galaxy S10, S10+, and S10e in parts of Europe. This brings with it the September 2019 security patches, alongside a bunch of new features: Night mode for selfies, Live focus video (which debuted on the Note10 family), Link to Windows, and DeX for PC support.
You'll also find the AR Doodle function in the camera app, but only for selfies, in video mode. All of these features are borrowed from the Note10 family, and it's good to see them making it to the S10 devices as soon as possible, without Samsung having waited to include them in the Android 10 update.
The update requires a huge 1.2GB download, and once you install it your phone will be on the G97xFXXU3ASIG firmware version, where "x" stands for "0" if you have the S10e, "3" if you have the S10, and "5" if you've got the S10+. As usual it might take a few days until you get to see this update, the rollout is staged and it's going on a country by country basis in Europe at the moment.
Source (in Dutch)