Thanks for the details, @Fern2.

I've got steps to help ensure you can find and open your company files.

First, let's locate your missing company file through the steps below:

1. Go to File, and then choose Open Recent to open the company file you last used in QuickBooks.
2. However, if you're unable to find it, you can go to Documents/ QuickBooks folder which is its default location.

For your major company file, we can either rename or move it to another location to fix the error.

To rename it, here's how:

1. Open the New Finder window and then locate your company file.
2. Go to the File menu, and then select Rename.
3. Create a new name, and then click OK once done.

To move your company file, follow these steps:

1. Open the New Finder window and browse to where your company file is located.
2. Go to Edit, and then choose Copy.
3. Paste the file to another folder or you can create a new folder.
4. Hover to Edit again, and then choose Paste.
5. Open your QuickBooks, and then pick Browse.
6. Look for the new location of the file, and then tap Open.
7. Then, let's delete the file from the original location by going to the New Finder window again, and then drag the file to the Trash icon.

Also, you may verify and rebuild your data to fix common issues within your company file. Please refer to this resource for more info: Verify and Rebuild for QuickBooks for Mac.

Feel free to get back to us if you have more questions about managing your company files or anything else related to QuickBooks. I'd be glad to assist you further. Take care and stay safe always.