Hi there, @GrumblePuss. I appreciate you getting back here. I'm aware of how difficult it can be to be unable to access your company file. I'll provide additional measures you can take in troubleshooting.

Sharing the steps you've performed is a helpful way for me to provide other troubleshooting steps you haven't tried yet. Since you've already ensured that your QBDT is updated, we can move your company file to another location and open it. Let me guide you on how:

1. Navigate to the Start menu and enter File Explorer into search. Then, open File Explorer.
2. Look for the folder with your company file (it’s usually in your QuickBooks folder. It looks like this: [Your company name].qbw.).
3. From there, right-click your company file and select Copy.
4. Next, right-click anywhere on your desktop and click Paste.
5. Once done, open your QBDT 2022 and go to File. Then, select Open or Restore company.
6. Find the company file you copied to your desktop and click Open.

If this works, the file location is the issue. That said, you have to move your company file to a new folder. If you share your file on a network, you’ll need to share the new folder. If the same thing happens, it might be due to data damage. To fix this, you can restore the recent backup of that company file.

To know more, read this article for reference: Can't open your company file in QuickBooks Desktop.

However, if the issue still persists, I recommend contacting our Technical support team to investigate the issue further. Once connected, you can also request a screen-sharing session so they can review your account setup. Doing so will help them identify the root cause of the error and guide you in fixing it. Here's how:

1. Open your QBDT program and select the Help icon.
2. Next, click QuickBooks Desktop Help.
3. Then, select Contact Us.
4. Enter a brief description of your issue (Example: Cannot open other company files in QBDT 2022) and select Continue.
5. Log in to your Intuit account and select Continue and then Continue with my account.
6. You'll receive a single-use code and input it. Then, click Continue.
7. From there, choose either Chat with us or Have us call you.

In the meantime, you can access your company files by manually opening them directly in the folder where they are located.

You're always welcome to post a question again if you have other concerns regarding accessing your company file. I can assist right around the corner. Have a good one.