This release introduces ray-casting in your games, access to a surface's depth and stencil buffers, the ability to place text in your rooms inside the editor (and manipulate it later on in-game, if you wish), a lot of new additions to the in-game debug GUI functionality, and more...
As well as all the new stuff above, this release has a large number of important stability, performance, UI/UX, and QoL fixes that should hopefully make things a lot smoother as you're using GameMaker.
Note also that there are quite a few important fixes for building projects, collisions, audio/Sequences functionality, and other things which may require you to have to now make some changes in your projects, so please do read the full notes carefully.
And for a little more on some of the headline features you can also see the release blog post.