Is there a way to enable diacritic marks for the course?
They seem like they'd make it easier to learn new words.
Do you mean nikkud/vowel markings? If so, then no. The Hebrew team explained that it's a bit of an all or nothing thing with the nikkud, they do appear in some sentences, but it is not practical to use them for every word when they're teaching Hebrew how it's actually used, which means not using nikkud and just getting used to doing without them.
Yeah, it's a bit of a pain in some ways, but it's basically to do wth how the Duolingo system works. I only know from second hand, I haven't seen it in the incubator, but my understanding is that if they wanted to use nikkud for individual words, then everything would have nikkud all the time and the system would require nikkud to mark answers correct.
I think there are some posts around where the team explained their reasoning... if you do a search in the Hebrew forum for nikkud or niqqud then you may find some stuff. I'm not sure, but I think it may also be mentioned somewhere in either the welcome post or the FAQ post.
It does get easier - I'm finding I'm getting better at making a stab at how new words might sound, and I'm adjusting to sometimes having to pick a word out from a sentence and note how it sounds. I think it's probably better in the long run!