This Error is only in VS2019. This Error never happens before. Idk if it was becasue i misclicked something in VS. In Unity there is no Error message and everything works fine, even playmode.
But when I open a random script that is using methods in MixedReality.Toolkit, there will be warnings that "***"(e.g, Interactable) is not a Unity Component, and error message that I am not using the toolkit or no reference(CS0246 error).
I not very good at coding so I don't know what can I do to fix it....