Hi again!
The point is, the flow you are working with triggers when a new file is created.
In order to perform a backup of current student files stored in Sharepoint, you need a manually triggered flow, that reads all files belonging to the student by means of 'Get files (properties only)' then do an 'Apply to each' to iterate all through the student current files in Sharepoint, and copy each file to student's onedrive.
The concept is explained here with flow design screenshots:
https://joannecklein.com/2018/01/02/a-modern-transfer-to-another-location-in-office-365/
The differece is inside Apply to Each:
instead 'moving' files from one SP libreary to another folder + deleting original file; your 'copy' steps are exactly the same as the ones you have in your current flow.
This second flow is easy to implement, but we need to understand which files in SP belong to current student, something still unclear to me... 'Gt files (properties only)' will provide all files stored in the library, so ... which are the ones in SP belonging to a particular student? Are they stored in one subfolder per student? Shall I rely on 'Created by' column metadata instead?
Hope his helps