I appreciate your posting your concern regarding the company file that doesn't contain data when accessing it through your QuickBooks Desktop Premier 2024 account, Lclarkcpa. Let me share details on how we can fix this. 

When upgrading to a newer version of QuickBooks Desktop (QBDT), you must also update your company files to ensure compatibility and functionality with the software.

To update your 2021 company file, ensure to save a copy of it on your computer. Then, kindly follow the procedures listed below. 

1. Make sure all users sign out of your company file.
2. Open your QuickBooks Desktop Premier 2024. Go to File, then choose Open or Restore Company.
3. Click Open a company file, then Next.
4. If you have a backup company file (QBB) instead of a company file (QBW), select Restore a backup copy.
5. Look for your company file, select it, and then click Open.
6. Log into your company file as the admin user.
7. Select Update Now.
8. When QuickBooks finishes, select Done.

Kindly check this article for further information about upgrading company files in QBDT: Update your company files to a new version of QuickBooks Desktop.

In addition, I'll be leaving this article for you to read through that discusses company file compatibility to evade errors when upgrading QBDT software: Company file compatibility with QuickBooks Desktop when upgrading.

Let me know if you encounter further difficulties opening your 2021c company file in your QBDT Premier 2024. You can reach out to the Community at any time, Lclarkcpa.