Tool Database - Cloud Version Selector
The Tool Database backups are kept separate for each major version (e.g. V10, V11, etc..). If you've recently upgraded from an older version (from V10 at least), you will not have your backup for the new version set up yet. This dialog will pop up the first time you attempt to download a backup.
It gives you the list of versions which you could download from. Those are the versions (products and versions) for which you've previously backed up your data for.
You can choose to not show this version selector again and always download the backup for your current version, which is most likely what you want to do.