B4A relies on Android's build in SQLite version. None (that I'm aware of) of the Android versions of SQLite include FTS5 support. You would have to bundle your own version of SQLite with your application if you want FTS5 support. A possible solution to including a newer version of SQLite is to use SQLCipher. It bundles a more recent version of SQLite and technically has the ability to support FTS5. B4A's version/wrap of SQLCipher can be found here: https://www.b4x.com/android/forum/threads/android-database-encryption-with-sqlcipher-library.14965/. It will be up to you to test that version and see if FTS5 has been enabled.