despite that the "Collect Addresses separately" feature allows for anonymity of respondents, a data processing agreement (DPA) is still to be signed.
On the one hand, the data in the questionnaire remains anonymous - therefore you can collect contact data separately on www.soscisurvey.de
On the other hand, contact data is personal data by itself. Therefore you need the online DPA.
Hence I am wondering if signing the DPA and proceeding with the usage will not interrupt/cancel the academic-free version of SoSci survey.
No it will not. But at the same time, the online DPA is strictly limited to address data. That means this DPA will not allow you to collect person-related data in the questionaire itsef, only separately.