Remember that Revit files are not backward compatible. If you save a project in Revit 2020, you can open it in 2021 or later, but you cannot open it in Revit 2019.
The trial is fully functional but expires exactly 30 days after installation. autodesk revit 2020 trial version download
If you don't see it in your account, use the Autodesk Assistant (the chat bubble on their support page). Type "Download Revit 2020," and the bot can often provide direct download links for versions up to 5 years old. Remember that Revit files are not backward compatible