it's one of the key features of the app that most other alternatives lack, it would be weird for them not to mention this
> And why do I need to login for an offline app?
it's not offline only, it can sync to your other devices over the internet
> Where does the data really go? There is some setting remote storage, and some mb already used, so is in reallity an online-app with some offline-mirroring?
it's stays on your devices, unless you pay for dedicated backups of your data
> and the saved files are just your usual electron-blob-files. Seems there is no way to really access or control my files externally.
your data is encrypted, which is why you can't just access it via your file manager
hope this helps :)