Updating the "New note" button is actually planned, because it's true that some people can't find it, and that's a big problem for a note app. Adding a plus is not a good idea though because it would be tiny at the real size
Maybe we need a huge "New note" button like Evernote as that would definitely solve the problem. The original design for the new Joplin UI had the "New note" text but it was removed although I forgot why (maybe just to make room for the search bar? But I seem to remember there was something else). Perhaps removing it was a mistake:
