Would using a newer version of Desktop for Accounts change a file from an older version where it cannot be used by client??

Glad to see you here in the Community, @liquakerlady.

In QuickBooks Desktop (QBDT), we're unable to downgrade a company file once it's updated. This means we won't be able to open your updated company file in the old version.

Though, we can restore a backup copy of your company file if you have one. Let's also make sure you and the accountant are on the same QuickBooks version or there's at least a gap of 1 year.
 

Here's how:

1. Go to the File menu and select Open or Restore Company.
2. Choose Restore a backup copy and then click Next.
3. Select the Local Backup radio button, and then click Next.
4. From the Look In drop-down arrow, choose the backup file location.
5. Locate the backup file from the folder. The file name should appear as [Company Name].qbb.
6. Select Open and then click Next.
7. From the Save in drop-down arrow, choose the location to save the restored file.
8. Type a new file name in the File name field then click Save.

For future reference, here’s a link that covers the troubleshooting steps when the desktop program is not working or frozen: Solutions for when QuickBooks has stopped working.

In case you need tips and related articles in the future, you can always visit our Community help website: QBDT Self-help.

Feel free to drop a comment below if you have other questions. I'm always happy to help. Take care!

@liquakerlady 

You have to purchase a 3rd party downgrade service. As long as there is no additional record in the upgraded file, we may revert it back to the old one easily. Otherwise, some data will be vanished.