Nice to hear from you again!
It's lawful for BAMF to collect all documents that they need to check your identity (passport, ID, drivering license etc.). And according to law they are also allowed to keep them.
Source (German language): https://www.gesetze-im-internet.de/asylvfg_1992/__15.html
I couldn't find any information about deadlines or something like that when they have to give it back to you though.
What advice did your lawyer give you?