Can I import quickbooks files from a flash drive loaded with files from my bookkeeper?

Yes, you can.

https://quickbooks.intuit.com/learn-support/en-us/help-article/import-export-data-files/move-quickbooks-desktop-file-quickbooks-online/L6af3Z0Fb_US_en_US?uid=mgnr7rny

You can also use the trial version of QB Desktop 2024 to access your historical data for good if required.

Hello there, ksheston1.

Yes, you can. As suggested by SIAB, you can use the free trial version of QuickBooks Desktop (QBDT) to restore the .qbb file, and then proceed to transfer it into QuickBooks Online (QBO). To restore your .qbb files, here's how:
 

1. Go to the File menu, then select Open or Restore Company.
2. Select Restore a backup copy, then click Next.
3. Choose Local Backup, and then toggle Next.
4. Browse your computer for your backup company file. It should look like this: [Your company name].qbb.
5. Select a folder to decide where to save your restored company file. Then select Open.
6. When you're ready, select Save. If you see any messages about possibly overwriting your data, select the option that best fits your needs.

For detailed information you can refer to this article: Restore a backup of your company file

Next, to import the PDF files or other QBO supported files to your account, here’s how:
 

1. Go to the Gear icon, then select Import data under the TOOLS column.
2. From the drop-down menu, choose the appropriate record type, and then click Import.
3. Find your files that you want to import, then toggle Next.
4. Provide the correct information needed in the fields.
5. Check everything, and after that, click Import.

For additional help, don’t hesitate to reply below by clicking the Reply button.