I'm pretty good at creating shaders in Blender, and I've made a few decent things in Unreal Engine as well. In GameMaker, shaders remain elusive. Why?
Well, Blender and Unreal both have intuitive methods for creating shaders. Blender has a node-based system where you connect different pieces of the shader program together and, based on how you do it, different effects are achieved. Unreal is similar, with a system called Blueprint.
GameMaker Studio 2, on the other hand, has none of this. If you want to create shaders in GameMaker, you have to either code them by hand, or find one that someone else has coded, and tailor it to fit your project. This can become especially difficult if you're not very familiar with GLSL, or you're trying to work from an example that was made with a different platform in mind.
I appreciate that it makes me think a bit more about what I'm doing on those other systems, and how to accomplish the things I take for granted elsewhere. I'm not very good at it yet, though!