Hello, welcome to the forum.
I don't know if the reason
apprentices/student in Bern need not reside in Zurich is valid or not. If you're appealing, you're quite probably in contact with a lawyer that have better knowledge on the topic.
What we do know for the experience of others is that canton Zürich has some issues on minimum income for B permits
https://www.englishforum.ch/permits-...-b-permit.html
Also, I cannot find the info right now, but it seems the emission of new B permits has been suspended during the virus crisis. Maybe other forum members can provide more details on this.