Hugo, to import your v10 project into the current version it needs to be imported to v11 or greater as an interim measure. You can contact me via https://esahc.com and we can work out how I can retrieve your project. I would import it into v14 or later and then return it to you so you can import in v2020 (no charge). Others here have also offered this service in the past.

You need to open your project in v10 and go to step 5 export project (do not include preview) to create the iwzip file.

Please be aware that much water has passed under the bridge since v10. Much of the underlying software has been replaced and some features work differently. Under many circumstances a better result will be achieved creating a new project with a new template and recreate the site by copying and pasting from your old online site. However, if there are a significant number of linked files, a blog, shop, etc the conversion could save many hours of work.