Backing up an NTSF drive attached to a Mac

I recently retired a Windows 10 machine that had a 12 TB NTSF drive of pictures, videos, and music attached that is 75% full. That drive was backed up to Dropbox on the Windows machine. I bought NTFS for Mac from Paragon so that the drive is writable on my Mac, and it works like a dream. Except where Dropbox is concerned. This NTFS drive was also my Dropbox drive on the old machine. 

I would rather not have to buy a new drive,  format it for APFS or HFS+ and then manually copy everything from the old drive to the new drive.  But it looks like if I want it to backup on my Mac, that is my only choice? (except format the existing drive and hope everything from Dropbox will be put back -- but that will take almost a week!) If I try and set the old Dropbox folder on that read/writeable NTFS drive on my Mac as my Dropbox folder, I get an error telling me that the format is not supported. Really? You support those kinds of files from a Windows machine, so I know they can be stored on Dropbox. So why can't you support the same file types on my Mac? It is just a file, and it is readable and writable on that drive. I belive this is a serious oversight by Dropbox software. Since all you backup is a file anyway, just backup the file! And I know you can backup an NTFS file on a Windows machine and then sync it to a Mac, and the reverse method works as well. So why shouldn't this just work! This is obviously a software limitation that seems unnecessary to me. 

Anyway have a workaround for this issue? I guess I could install VPC on the Mac, and then switch operating systems when I want that drive backed up, but kind of defeats the purpose of Dropbox always keeping gone backed up, and switch the OS is a pain in the &**( and takes a long time. 

Dropbox: How hard would it be to set NTFS files and legal files to sync on the Mac? This might be a time I stop using Dropbox and go to Cloudflare or some other cloud backup that knows how to support multiple file systems on a Mac. Disappointed by what is otherwise excellent software.