Hello Tanja,
If you use the cloneable date field in a cloneable group, the data is saved to the database in a serialized format (array). So if you want to query posts by date field, you can follow the tutorial in your post, use the single cloneable field and enable the setting Clone as multiple
to get a single value per row in the database.
Also, please note that, in case of using Bricks Builder, please reach out to them if you have any issues with installation, configuration, compatibility, or usage.
Refer to our support policy https://metabox.io/support/topic/support-policy/