Backing Up Company File?

Thanks for posting here, @Kelly6. It's good to know that you already verified the data to isolate the issue. 

Let's work together to resolve the error so you can back up your company file in QB for Mac. 

First, make sure that your QuickBooks for Mac is updated to its latest release. This is to make sure you have the latest features and fixes. See this update for the latest release. 
 

If the same thing happens, try to verify the data again, then run rebuild to resolve it. Follow the steps below for the process.
 

1. Open your company file again.
2. Go to the File menu, then select Utilities and choose Rebuild Data.
3. Click OK in the QuickBooks Information window.
4. Wait until the repair is done. Then, click OK.
5. Then, go back to the File menu and select Utilities and choose Verify Data.
6. Click OK if QuickBooks doesn't find any problems. Or Rebuild Now if it finds issues with your company file.
    

Here's an article that details the steps: Fix data damage on your QuickBooks Desktop company file. 

Also, this issue can also be caused by attachments being backed up along with your company file. Another workaround is to backup the company file itself not including the attachments. 

Here's how:
 

1. Open your QuickBooks Desktop
2. Go to Preferences and select Backup
3. From there, unchecked the Backup attached documents library.

If everything is fine, you can then create a backup of your company file. 

I'm also attaching this article if you need to undo recent changes in your company file or lost your data: Restore your backup company file for QuickBooks Desktop for Mac. 

Should you need further assistance with backing up your company file, feel free to leave a comment below. I'm always around to help. Stay safe and have a nice day!

@Kelly6 

How big is your company file size?

Try opening the sample file. Can you create the backup file?