Converting the QuickBooks 99 to Desktop Pro 2020 is unavailable.
We can only convert QuickBooks 2016 file as the oldest version, lower than that we can no longer transfer data to the latest version.
I will not leave you there, though. I'd recommend to try searching a third-party application that will help you convert the QB 99 to the latest one.
Also, you may want to take a look at the benefits of the QuickBooks Desktop 2020 features. This article will talk on how these features will help your business grow.
Please get back to this thread if you need more information with the QuickBooks 2020. I'm always here.