Your journal and your progress live in this browser’s storage, nowhere else. That is a deliberate choice: nothing about your study is sent anywhere. It also means clearing your browser’s data, switching to a new phone, or even just switching browsers can erase months of work in one click, with no warning and no undo.
Settings has an answer for that, one row per study, under both Journal Data and Progress Data.
Export saves everything for that study as a single JSON file. Import reads that same file back in, whether on this browser or a new one. Nothing else is a valid import file; only what Export produced.
Make exporting a habit, not an emergency measure. Before you clear your browser’s cache, before you hand your device off for a repair, before you switch phones, export first. It takes five seconds, and the alternative is starting over.