Sync Onedrive to External HDD

I might wasn't clear.
I need to backup all files I have to OneDrive and currently syncing with my PC with its SSD drive.
Those files are important and I need to have an extra copy just in case anything happens.

What I had in mind is to plug in the HDD, perform a sync (meaning that I will keep local / fully downloaded copies of course), deplug the HDD and store it at a safe place.

OneDrive should continue working with the SSD after that.
Every month, I would plug in the HDD again and perform the same syncing backup action again.

I couldn't find anybody else who had the same question. If that slipped my attention, please let me know.
Thanks