Turns out, the *.rs file needs to be in some kind of folder structure, like the one provided by cargo when creating a project. I was just editing the loose files in the rustlings program, and because they are not in a proper program folder structure, most of the syntax stuff didn’t show up.
Thank you for sharing your experience though! It was very useful for figuring out if what I had was an issue or normal behavior. Now my neovim works perfectly with all the syntax highlighting I could wish for.
I’d like more pixels please. Literally can’t read it…