We collect absolutely nothing if you're syncing with iCloud.
Everything you do is saved to your iCloud and is synced across your devices using the same iCloud account. However if you opt for Tasks' Cloud which is optional and not selected by default, we sync your data in a secure and confidential manner with our private servers and is not shared with any 3rd party service.
If you have any questions at all, about your data or any other query, kindly contact us. We are happy to answer everything!