thanks for getting back to me so quickly.
By the way - there is also a comment option on our platform, so that your answer appears on the same thread!
Here is the link to the first thread you started: https://www.wefugees.de/802975/with-only-father-serve-have-chance-to-get-permit-stay-germany
Have you had a look at the sources I looked up for you already? Especially the other thread that had been answered on Wefugees provides a good answer similar to your question. The full answer:
"As a father of an underage child who does not have the German citizenship, you can try to apply for a residence permit, but you´re not entitled to get it granted. The decision on your application is at the discretion of the immigration office.
The residence permit is usually granted only if the family unity between you, your child and his mother can only be conducted in Germany. It must be unreasonable for your child and his mother to follow you to your homeland. According to the Federal Administrative Court, the fact that a family member, in this case, your child and his mother, has a residence or settlement permit, doesn´t preclude a joint departure and doesn´t justify a ban on deportation.
So if you want to apply for a residence permit in this situation, you will need to mandate a lawyer to submit the application for you."
As I mentioned before, it might be best in your case to consult a lawyer and discuss your options if you can get a residence permit, or have a look at the pro bono legal advice services in your area to receive some help.
All the best,