Binding \Cj also rebinds <Return>
Apparently \C sequences are stored as integers, and \Cj happens to be 10 (the same as ) so binding: bind index,pager \Cj sidebar-next prevents the Enter key () from working as it also binds it to sidebar-next. Also reported/probably better explain, here: https://github.com/neomutt/neomutt/issues/1448