Samsung's most recent update to the Expert RAW app seems to have added astrography mode to more than just the Galaxy S21 series. The Galaxy Z Fold 4 also supports the mode with Expert RAW version 2.0.09.1, which was released on the Galaxy Store late last week.
Samsung had confirmed a few months back that it would be bringing the astrophotography mode to devices other than the Galaxy S22 and Galaxy S23 smartphones. The list of eligible devices include the Galaxy S20 series, the Galaxy Note 20 and Note 20 Ultra, and all Galaxy Z Fold phones except for the original. And with the Galaxy S21 and Galaxy Z Fold 4 getting the feature with the latest update, we're guessing the other eligible devices will also get it soon.
With astrophotography mode, you can point the phone's camera at the night sky and get high-quality shots that capture the stars and constellations, provided you have clear skies not ruined by pollution in your area. Expert RAW also pinpoints the location of constellations to help you, and you can set an exposure time between four to ten minutes.
If you own a Galaxy Z Fold 4, you should be able to download the latest Expert RAW update from the Galaxy Store. The app itself should also notify you there's an update available when you open it. Once installed, just tap the last button at the top right of the screen to start taking astro photos.