Then, install a trial version of QBDT Pro 2016 and restore the backup file, then create a new backup. First off, you can download a trial version of QuickBooks Desktop (QBDT) Pro 2012, then restore the file, then create a backup file. In doing this, you'll have to restore the 2008 file in 2012 > 2016 and then 2020. This way, you'll be able to move and restore your file. To get your work done, you may upgrade QuickBooks to the latest release.
Thank you for joining us here in the Community for your installation concern, mentioned by Mark_R above, the oldest version that we can install is 2012.