Thank you very much for your question and Welcome to the Wefugees community!
Since you ask about the certificate of no impediment/ Ehefähigkeitszeugnis, I believe this link from the Berlin service website is quite helpful: https://service.berlin.de/dienstleistung/318993/
Here is another link from the Standesamt Nürnberg answering important questions about the certificate: https://www.nuernberg.de/internet/standesamt/faqefz.html#2
(Both are German sources)
To me it looks like it would be best to go to/ call your responsible Landesamt or Standesamt to ask about all the documents you will need in order to get married abroad and how to make sure the marriage will be fully recognized in Germany (because there are some countries where a certificate of no impediment is mandatory to get married, so also remember to check the requirements in the specific country you want to marry in).
I hope these sources help to answer your question.
Do feel free to reach out to us again if you need any further assistance!
All the best,