I know you said in game preferably, but I do think it’s worth giving a shout out to Nobbel on YouTube; his lore videos are really engaging and thorough, and you can often find videos on specific topics (like the story of Sylvanas) where he compiles history from several sources into a video. It’s worth a look if you’re really interested in the lore, because for better or worse the game itself sometimes only touches on events that have more depth in other sources.