APK, XAPK, and OBB Files and ModJoy APK: A Guide for Low-Storage Android Phones

https://gamemoddepot.nexorafield.com/posts/why-understanding-package-signatures-matters-when-exploring-apkmodjoy

On a phone with little free space, every download and update needs a little more planning. APK, XAPK, and OBB labels describe different ways Android apps and large game assets may be packaged or delivered