I just tested every theme, and the font "" appear just fine for me, not as rectangles? Are you copying and pasting it from a word doc or something like that? Just curious!
I mean, it does support curly quotes when I do it like """""
But it doesn't support smart quotes, which is created from MS Word and the like? So not sure it should be an issue if you're not copying and pasting? Unless your keyboard is cooler than mine and supports things mine doesn't lol. The same with the EM dash, you listed above, I think.