Are you new to Windows, period? I only ask because File Explorer has not changed significantly for a very long time now, and if you knew how to use it before virtually everything you already knew should carry over.
There is absolutely no reason, in general, to use Object Navigation in File Explorer. It is entirely accessible via "the more usual means."
I am not quite sure what you're asking with, "Is using the Windows shortcut keys the only way to navigate the File Explorer?" As a broad, general answer it's, "Yes." There are few, if any, screen reader specific commands used for File Explorer. It behaves similarly, using standard Windows Shortcuts (which include TAB and SHIFT + TAB, among others) regardless of the screen reader you are using or whether a screen reader is in use at all (although most sighted people have no idea about those keyboard shortcuts - they're way more likely to point and click).
It would help if you could give a short list of what you can't do that you want to be able to do in File Explorer. This is such a fundamental component of Windows that it's generally taught as part of a "Windows for Newbies" class of training, which is why I asked if you are competely new to Windows.
I would also strongly advise you to consider joining the Windows Access for Screen Reader Users Group if you are new to Windows. The questions it appears you are most likely to ask really aren't about the screen reader, any screen reader, but about accessing Windows components, in this case File Explorer, with Windows keyboard shortcuts/commands.
Windows Access for Screen Reader Users Group (Formerly: Windows 10 for Screen Reader Users Group)
Group Archive: https://winaccess.groups.io/g/winaccess/topics
Group Owner: firstname.lastname@example.org
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
The difference between a top-flight creative man and the hack is his ability to express powerful meanings indirectly.
~ Vance Packard