If you want to author runtime UI, you need to install the UIToolkit package as well. Read “How to get started?” in the following thread for the instructions:
Hello, if I’m seeing correctly you don’t have the UI Toolkit package, can you confirm that you followed the steps on the announcement thread to install it? It’s about modifying the manifest to contain the reference to the package (currently version 1.0.0-preview.6).
I got it working. For anyone else reading this thread with a similar issue:
I had to manually modify the packages.json to include:
“com.unity.ui”: “1.0.0-preview.3”
When I restarted Unity there was an error saying something about a duplicate dll:
UnityEngine.UIElementsModule.dll
I located the dll in /ProjectName/Library/ScriptAssemblies/ and moved it into a directory outside of the Unity project, relaunched, and it worked. One error popped up, but it cleared without further issue.