While Ren'Py games often package everything into a single APK, the size of Summertime Saga has historically been a hurdle. In some distributions of older versions, users might encounter a split setup where the APK is small, but the game assets are stored in an OBB folder. If this is the case for the specific 0.18.6 build you find, the OBB folder must be placed manually in the Android/obb/ directory on your device's internal storage. Failure to do so results in a black screen upon launch.
Key fixes included: