If you clear this app's data, switch devices, or uninstall, everything is gone. There is no cloud backup. There is no account. The browser PWA and the Android app each keep their own separate data.
What you must do:
Visit DATA + SETNG → BACKUP & RESTORE regularly
Hit EXPORT — it downloads a CSV file with all your data
Save that CSV somewhere off this device (cloud storage, email it to yourself, anywhere)
Do this at least once a week
If you lose your data, IMPORT the CSV brings everything back