I was for example surprised to learn that Mind Flayers are protected, like the whole race and all it's properties. Dwarves and elves are not. I think anything Underdark, including Deep Gnomes, Duergar and Drow are also protected. There are probably certain magical items that are also protected, like the Immovable Rod, or Ring of Feather Fall, etc.
For home games none of this matters of course. But I'm certain it's going to be problematic for players that want to stream their play sessions, creators of other media like games or boardgames that want to make something D&D-adjacent-but-not-such-that-it-awakens-the-dragon and so on.
Also, for things like "Dwarves and elves", that'd be a bold move on their part. As so much of the original D&D was poached from a variety of sources (see Appendix N [1]) they need to be careful if trying to claim those.
But obviously there's also a second layer where you can't publish your own novel about, say, the intricate details Drow matriarchal society, that aren't in the SRD and came from WotC novels and sourcebooks. Presumably it's a bit like with Sherlock Holmes, where the character himself is out of copyright but certain lore details added in later books are still covered.
