I went straight from Processing to Rust. You’d be surprised by just how many skills transfer over! I’ve found that it’s actually easier than other programming languages, aside from doing anything visual. I haven’t figured out how to do the same kind of graphics stuff as i could in processing just yet.
As for use cases? Processing is a learning tool, and it’s great for teaching as well. You can make some pretty great animations using it, and a lot of YouTubers use it internally to animate their math videos.