SMAPI APK Android Installer is an APP which can install the SMAPI for Android, which makes it supports mods. Stardew Valley and mods should download separately, installer just supports to prepare mod environment and mods management.
The Android version of the game is very custom compared to other platforms, so the official version of SMAPI isn’t compatible. There’s a port of SMAPI to Android developed by MartyrPher and later ZaneYork . It supports most SMAPI mods and content packs (including framework mods like Content Patcher, Farm Type Manager, Json Assets, and PyTK), but some mods may not be compatible.