Are there any 3D engines for scratch? I know there are a few already out there, but they're usually many years old. Are there any newer engines that have better shadows or more features? I tried using this one but it was hard to add any new features and had some issues with rendering.

Yes, there is. In fact, I have made 2 of my own.
Here is my pen-based one: https://scratch.mit.edu/projects/630905610/
Here is my clone based one: https://scratch.mit.edu/projects/615121828/
The pen-based one is easier to use.