How do you use a turbo frame to replace an object creation form with an object show partial?

This is documented in the docs. See here.

Yes. That is possible, the form that ultimatly calls the create action on the server can have a data-turbo-frame to tell Turbo to replace another frame rather than “this” frame the form is in.

 <%= form_for ...., data: { turbo_frame: "frame_you_want_to_replace" }