My Book Duo - Bought new MAC and I cannot drag files to it

I am not a very tech savvy person, just FYI.

I had a 2012 Macbook Pro, the video card died and I bought the new MacBook Pro which now has the new hook-ups and I bought an adapter for the USB port. On my old MAC, I was able to transfer files, no issues. Now with my new MAC, it is not letting me back up anything, no drag and drop to the external HD. I can, however drag files from HD to my laptop.

Anyone familiar with this problem?

Thank you.

Is the drive formatted either exfat or hfs+?

I formatted it as Mac OS journaling. To get my new computer to work with the HD, I made sure all was backed up and reformatted it the same way. Then it was only letting me upload 2GB at a time. So I reformatted again.

Now the Hard drive does not appear on my desktop and it appears to be full.