Last week we help our client to convert their QBW file of Pro 2013 to Pro 2020 easily. It just converted completely without any effort. They were opening the converted file on trial license of Pro 2020 and migrating it to QB Online
We are not sure yet which the oldest version (year) we are able convert directly to 2020. You may install the trial license of Pro 2020 and try open your file on it. Once it is converted, you may migrate it to QB Online. Make sure to click the Buy button to get the discounted price for up to 6 months. If you purchase from the trial account, you have to pay the regular price.