It’s called HDR (High Dynamic Range) photography. Your phone is taking three pictures: one at a medium exposure, one at a bit higher exposure and one at a bit lower exposure.
The higher exposed picture will have a blown-out sky, but more detail in the darker area, while the lower-exposed one will have a correctly exposed sky with the darker areas underexposed.
These pictures are then combined by taking the correctly exposed areas of each picture, i.e. the sky from the low-exposure picture and the shadows from the high-exposure one, giving you a single picture without over- or underexposed areas.
I don’t know about OpenCamera, but you should be able to select the size of the exposure bracket, meaning how much higher or lower the different pictures are exposed.