When creating a shipment, the checkbox "Create shipping labels" is missing.
Checkbox "Create shipping labels"
The country of the shop is not set correctly (unsupported country).
The shipping method for the order is not selected in the DHL configuration "Shipping Methods for DHL Versenden / Shipping".
The shipping method is not compatible with DHL Versenden / Shipping, because its real name does not exactly match the name shown in the box "Shipping Methods for DHL Versenden / Shipping".
The buyer's address couldn't be detected automatically (splitting street name and house number)
DHL Easylog is installed on the system.
Set the shop's country (shipment origin) correctly. The supported countries are listed in the documentation, section "Hints for using the module -> Shipping origin".
In the configuration "Shipping Methods for DHL Versenden / Shipping", select shipping methods that should be handled by DHL.
Check if the affected shipping method has an extended name in the background (different from the one visible in the browser). This can be checked with the browser console (DevTools) by looking at the shipping method element in the checkout. Look at the value for <label>.
Click the link "Edit" at the shipping address and correct any mistakes. Make sure to enter the street name and house number separately into the special DHL fields further down on the page. For further details see this article.
DHL Easylog must be removed completely from the system. Otherwise, it can disrupt the process of DHL Versenden (Shipping).
After resolving the problem, create a new order to test if it works! For the existing orders the checkbox will still not be displayed. Those orders need to be re-created if necessary.