It does sound like a permissions issue. Locate one of the files that won't open up in the Finder. Then copy it to your Documents directory on your main hard drive. Once you've done that, drag the copied file onto the QuickBooks Mac application icon and see if it opens. If it does the issue is permissions on those external hard drives.
You can also examine the permissions on a file by selecting the company file in the Finder and choosing File->Get Info. The permissions are down on the bottom. QuickBooks needs both read and write permissions for the current logged in user .
There is a macOS option to open up permission access on other drives. I think its accessible by selecting the drive on your desktop and then choosing File->Get Info. There's a checkbox for "Ignore ownership on this volume". If that's off you may want to try turning it on.
It could be something else, too, but given the many hard drives lets start there.
Thank you for all your help I did get it open for some reason it moved a file from my old drive after it was open in in the other OS then took that drive out of the mac made sure it opened in the old OS Then I replace the App in the new OS with old Mac OS , then I started Mojave back up and it worked