UI not found in UnityEngine

Unity Engine
1

The type or namespace name ‘UI’ does not exist in the namespace ‘UnityEngine’ (are you missing an assembly reference?)

I get the above error in my project.
I had previously deleted the library folder and tried to relaunch my project.

Is there something I’m missing? Anyway I can reset my project?

More Info: I’m using Unity 2019.2.15f1

2

I guess it’s too late, but in case anyone else has that problem and none of the solutions online work, check if your project folder is set to “read only”. Uncheck it if it is, then restart the editor. Hopefully, that helps.