(From this reddit thread for the Galaxy s10.)
- Download this zip: GCam.zip.
- Open My Files, find the Gcam.zip (probably under Internal Storage/Downloads/) then tap the GCam.zip, click Extract, then press Back, and you should see a GCam folder. Long press that, select Move, go back to Internal Storage, click Move Here.
- Open Google Camera, double tap the black space around the shutter button.
- March patch: Select S10csMar2.xml and Restore. Now when you cycle the camera switch icon you'll get the wide angle sensor eventually.