Hi @franziskandar ,
You can define a control group at the delivery level, in which case the control group will be applied to each delivery of the campaign concerned.
By default, the control group configuration defined at the campaign level applies to every delivery of that campaign. You can, however, adapt the control group for individual delivery.
If you have defined a control group for a campaign, and you also configure it for a delivery linked to this campaign, only the control group defined for the delivery will be applied.
Source: link
Br,
Shubham