You'd be glad to know that QuickBooks Online automatically backs your data up, and there's no need to save it on a flash drive or on your computer. I've got an article that provides more details about this: Do I need to back up my data with QuickBooks Online?.
QBO does not have a back up at all from the user perspective. And when you close your account Intuit will only save the company data as a read only file for one year, then it is deleted - which does not help if an audit occurs in year 2 or 3.
Intuit backs the servers up, but can not restore your specific file from that back up
US Versions ONLY: Both of the QBO export options to the desktop do not work accurately, not everything is exported, inventory item types are changed with no history, payroll checks are just expense checks, and the make local copy can not be used or opened from desktop. These known problems have existed for over 9 years. https://community.intuit.com/articles/1145409-export-limitations
All Versions: The only real option to get all your data for archiving against a future audit is to have an accountant log in and print or export to excel the general journal. (Or invite yourself as the accountant, create the log in, and log in as the accountant so you can use the accountant tools.) Due to QBO's limited data handling capability that will probably have to be done in date segments. Of course that may not help in the event of an IRS audit since they have stated that the actual software data file is what they want, and an excel spreadsheet is not satisfactory.
(Note: simple start does not have a true general journal report at all.)
QBO data handling capability for reporting is not adequate, if there is more than 5K records it times out and reports that you have too much data. You will have to do a journal report in date range segments, like Jan-Feb, Mar-Apr, etc etc.
How many months you can span per report is a guessing game since the report can not deal with more than 5K transactions.
Note that in the app store there is now some "backup" apps you can subscribe to, one subscription per company file. What these do is take a "snapshot" of your QBO data so you can restore it if needed. But in terms of a standalone back up file that you can access, or save against a future audit, no there is none.
I found FlexQuarters that has an application called QXL that will export all of the online tables/data to Excel. We use this for backup as well as additional reporting. This might be an option for some.