When I open a dtsx file in Visual Studio Enterprise 2017 it opens them as just an XML file. I read over this stack overflow discussion but when I do a File->New Project I don't see Integration Services Project as an option. I checked the Visual Studio Installer and I see that Data storage and processing is already installed. SQL Server Data Tools is checked too:
Is there something else that I need to do?
You may have installed SQL Server Data Tools without checking the Integration Services from the installer.
Also try using the standalone installer (check the link above for more details)