@bjornkummeling , Profile substitution is not directly available in the parent delivery. once you set up the workflow and the re-occurring email using no aggregation, at the schedule of your email delivery select request confirmation before send.
Then use the below steps,
start the workflow
it should show as sending started.
then click on the three horizontal dots in the corner
from the execution list select the delivery
in this delivery you can add profile substitution via Audience and test the delivery proof.