Upgrading to Quicken 2020 Deluxe

I would try a couple of things.  The first is to reinstall Quicken 2008 open your 2008 data set in Quicken, then run Validate and Repair on it.  That is provided that you have the install for Quicken 2008.  You might also need to blow away these folders if they exist to get a clean uninstall before installing Quicken 2008.
C:\Program Files (x86)\Quicken
C:\Users\USERNAME\AppData\Local\Quicken
C:\Users\USERNAME\AppData\Roaming\Quicken
C:\Users\USERNAME\AppData\Roaming\Intuit\Quicken
C:\ProgramData\Quicken
C:\Program Data\Intuit\Quicken

Once that is done. There are two paths to Quicken subscription no matter what the article says.  One is like it says and use Quicken 2013 as an intermediate conversion.  Another is just let Quicken subscription convert your Quicken 2013 data set directly.

The Quicken 2013 install and the article were placed there because of an early bug in Quicken 2014 that prevented it from upgrading Quicken 2009 and below data files.  But they fixed that problem with a later patch.  And as such all the versions of Quicken are actually able to convert data files all the way back to Quicken 2004 data files.

Come to think of it you might try a direct conversion from your Quicken 2008 data files to Quicken subscription to see if it is different.  But in reality it shouldn't be, but what tends to be the problem is there is some kind of problem in the data file that is hidden and the conversion brings it out, so that is why running Validate and Repair on it with the original version of Quicken might help.

BTW there probably isn't any reason why you can't run Quicken 2008 on a Windows 10 machine.  So one path might be to uninstall Quicken subscription, and reinstall Quicken 2008 and open your Quicken 2013 data file.  And then just get a refund for Quicken subscription. But for the reasons (problems might hidden) I would tend to really try to just get the problems fixed and at least go to Quicken 2013.

And Quicken 2013 might be the perfect version for you because it is the last version where non Quicken Id is required.  Which means it is the last version of Quicken that can be installed on a new machine without contacting a Quicken server.  The Quicken Id is free, but if Quicken Inc ever went out of business it would matter.  The subscription is on top of the Quicken Id and have ramifications like taking up 25% of your window with an ad to renew if you have let the subscription lapse.

Note you will want to install the latest Mondo patch for any of these older versions of Quicken.  You can find them here:
http://www.quicknperlwiz.com/quickenpatches.html