Okay, that is a quick jump from 3.0 to 4.0. I'm making a big version number leap because I want to make it clear that from now on I don't support GMS1.4 any more. The 3.0 release was the last GMS1.4 specific version.
There are no major features. Only conversion, clean up and bug fixes. All UI components have been validated to work with GMS2.3. I had a lot of drawing issues I had to fix with different vertex formats but those should all be solved now. If you do still stumble on any bug, please file an issue on GitHub.
I hope I've finally modernized the asset so more people are wanting to use it. I was afraid that people weren't using it because it doesn't work with the most modern IDE. We we'll see how much that plays a roll. Subsequently, I will be rolling out new GMS2.3 specific tutorial video's to accompany the written tutorials.