Hello there, LKSSF.
In QuickBooks Online (QBO), you're unable to do a backup of your company file. This is because QuickBooks automatically do it for you with the same level of security used by banks and financial institutions. And whenever you make changes to your file, your data is saved to two hard drives to protect it in case something happens.
For more details, check out this article: Do I need to back up my data with QuickBooks Online?.
If you're using QuickBooks Online Advanced, you have the option to do a backup of your company's data. To know more about it, check out this article: Back up and restore your QuickBooks Online Advanced Company. But if you're using a different plan, you may consider upgrading your QuickBooks Online edition.
If you want to export your data for safekeeping or use in another system, you can use the Export Data feature or look for a third-party application.
Let me know if you have other concerns about managing your company files and transactions in QBO. I'm always here to help. Have a great day!