In short, yes your drawings are private. We take your privacy very seriously.
The Concepts team does not have access to your drawings (unless you email them to us or share a link from a cloud site - e.g. you very deliberately share them with us). Concepts does not have its own cloud service for drawings. It depends on the platform you are using and how you are set up as to where your drawings are stored by default.
On iOS: with the 6.12 release, drawings default to being stored in your personal iCloud drive. You can change the location of your drawings by instead using the On My iPad section in the gallery sidebar, in which case your drawings are stored on your device. If you used a release before 6.12, then your drawings will continue to be stored locally until you move them to your iCloud drive (if you choose). If you configure iCloud Backup (recommended) then your whole device is backed up to iCloud and this includes your Concepts drawings too.
On Android: your drawings are stored on your device. If you configure Google Drive backups then they will also be stored in your personal Google Drive. With the 2024.3 release and newer, you have the choice of using application private storage which only Concepts can access, or internal storage which any file manager app can access via your Android Documents folder.
On Windows: your drawings are located in the Documents\Concepts folder. Whether this is synced to the cloud depends on how you have set up your PC. Any folder can be synced to most major cloud services if you choose to set that up.
Please review our Privacy Policy here. If you have any additional questions or concerns relating to the privacy of your work or information, please do not hesitate to reach out to us at privacy@concepts.app