Please branch and build python-nbconvert in epel9. If you do not wish to maintain python-nbconvert in epel9, or do not think you will be able to do this in a timely manner, the EPEL Packagers SIG would be happy to be a co-maintainer of the package; please add the epel-packagers-sig group through https://src.fedoraproject.org/rpms/python-nbconvert/addgroup and grant it commit access, or collaborator access on epel* branches. I would also be happy to be a co-maintainer (FAS: jonathanspw). I can be the primary contact for EPEL (FAS: jonathanspw).
*** This bug has been marked as a duplicate of bug 2158488 ***