There is a DGML Viewer in Visual Studio 2019. You can install it via Visual Studio Installer. Just open Visual Studio Installer, click on Modify, select Individual Components, Code Tools, DGML Editor. To create the DGML files from a DbContext on an EF Core application, you can use EF Core Power Tools. The image below is from a DGML generated by EF Core Power Tools and viewed using DGML Editor. I hope it helps.
