"Nested layouts" just sounds like nested React components.
React is kinda weird… you have to do subcomponents the "React way" and I think a lot of folks struggle with that; it can feel like fighting. But I don't think Next makes that any easier or harder.
I don't know what you mean by "nested routes." Routes are just URLs that map to files. You can create a directory with files, and, uh, subdirectories with files, if you want…?