You can take a QBW file from QuickBooks 2008 to QuickBooks Desktop supported version like QuickBooks 2019 or 2020 before you can load it into QuickBooks Online.
However, you would need a third party application or back up and restore the files to rebuild for each earlier versions. For example, the data would need to go to QuickBooks Pro 2011 - 2014 - 2017 - 2019. It's because it's the database of each product system requirements is modified as you update it. You can contact our Technical Support Team so they can help you install the lower versions temporarily.
Please know that there are limitations when you convert your file. That includes the attachments, audit trail, and recurring transactions. Once done, I'd recommend running the Profit and Loss and Balance Sheet reports to ensure that you transferred your data correctly.