Retrieve data without logging in (iMac G4)

Howdy. I am unable to log in to my family’s old iMac G4 for reasons outlined here: Accounts pane does not appear (iMac G4). I am considering factory resetting the computer so that I can log in with a brand new account (hopefully that will work) but I don’t want to lose all of the precious files in the process (all our old photos, music, etc.).

Before I factory reset, is there a way to transfer our old files from the G4 onto a newer computer / external hard drive without being able to actually log in? I am considering getting a Firewire > Thunderbolt adapter to connect to my 2015 MacBook Pro but I don’t know if I’ll be able to actually transfer files without logging into the G4.

Any tips would be appreciated!