Is there a freecodecamp for back-end coding??
Yes, there are other curriculum that cover backend here at FCC.
They are under Apis And Microservices Certification & Information Secuity And Quality Assurance Certification.
As mentioned, FCC does have back-end lessons. If you are looking for a different curriculum that teaches other languages, then all I can say is that I have never found any online program that is anywhere near FCC’s league.