Varies a ton between apps, some use private app storage on Android too (only accessible with root) or in appdata storage (restricted to system apps), or in scattered folders under the regular "user data" folders (easiest by far)
Bonus points if you have an SD card, double bonus points if you manage to have 2 of them, because then you have multiple copies of these standard user data folders
A lot of these laws have to do with expected lifetime in "worst plausible storage conditions", like poorly sealed boxes and wrong temperature and humidity