No sadly it will not be the night mode you are thinking of to change the theme to a dark friendly version.
Samsung will be pushing out an update by the end of April to early May to add the new feature. It will also include new software fixes also. The new Night mode for Samsung will be a feature added to the camera. It will be presented as a competitive feature to battle the Pixel’s Night Sight. At the current time S10 can take night photos but only when the device sees the conditions fit to do so. The new version will include the ability to turn it on whenever you wish.
The above image is from recent screen shots of the new update. If you are lucky and in Switzerland at the moment you can get the update by going to Settings > Software update. For the rest of us we will have to wait.