There is a massive bug going round right now with the DE hotkeys, where they have corrupted for a lot of people, and turned into the classic hotkeys: Changing Hotkey Defaults does not work, stuck in "Classic Hotkeys" and can't switch to "Definitive Hotkeys" - #17 by Kabcr
As far as mods go, the only real must-have mod for most people is small trees, I think, which isn’t linked to any event or anything.