Thank you for joining us here in the Community for your installation concern, @Peter_Martens_BRNL.

As mentioned by Mark_R above, the oldest version that we can install is 2012. To get your work done, you may upgrade QuickBooks to the latest release. This way, you'll be able to move and restore your file.

In doing this, you'll have to restore the 2008 file in 2012 > 2016 and then 2020. First off, you can download a trial version of QuickBooks Desktop (QBDT) Pro 2012, then restore the file, then create a backup file.

Then, install a trial version of QBDT Pro 2016 and restore the backup file, then create a new backup. 

Once done, you can now restore the new backup file to your QBDT Pro 2020.

Also, please know that it's important that your computer is compatible with QuickBooks to utilize the program smoothly.

On the other hand, you may check out a third-party application that supports the installation of the QuickBooks Desktop 2008 version.

Know that I'm always around to help if you need anything else. Have a nice day!