Why is Resources.Load failing to Load UI Prefabs?

Basically im trying to load a Prefab into the scene via path(I know bad style). it works fine for everything that is a normal Game Object, like a plane with a texture. But as soon as i try to load an UI Prefab,or a Game object wiith a rect transform it fails and just returns null.

Im using Resources.Load() + a path and then try to instantiate the game Object, like in the Documentation shown: https://docs.unity3d.com/ScriptReference/Resources.Load.html

I spend countless hours searching, nobody seems to have the same problem. Instantiation is not the problem, as it works if i drag and drop the prefab into the editor.

Any Reasons for this?