We actually don’t gather our users’ data.
But if you want to sync your data across devices, you’d have to upload your data (though we’re trying to move to iCloud for this so we don’t have to keep it).
Our privacy policy is available on our website and on the app before you login/signup, and we make sure to handle the data according to GDPR rules (though parts of GDPR are a bit lax, so I’d like to say better), considering it’s illegal not to :P