Hi @Islito
The information you have is correct. You cannot get the residence permit 25,.5 as an asylum seeker. The permit 25.5. is for people who have had the temporary paper called a Duldung for at least 18 months and who will continue to stay in Germany.
You do not have an automatic right to a residence permit on the basis of your girlfriend or son. The residence permit 36 is for other family members but this is only issued in cases of exceptional hardship. It is also not possible to receive this permit while you are in the asylum process.
If you receive a negative decision in your asylum case, then generally a person in your situation will be given a Duldung as long as you have an ongoing relationship with your son. As I wrote above, after 18 months with a Duldung you can apply for the permit 25,5.
Best,
Éanna