This is not a huge gripe in the grand scheme of things, but one of the few downsides of the DOS2 experience for me has been the ease with which you can not just miss whole plotlines, combats, etc, but *have those plotlines and combats completely cut off* by actions that give you no such warning.
The two worst examples so far: 1) if you walk past certain points on the map before finding Gareth and Jonathan, Gareth and Jonathan vanish from the hut and Gareth's parents die, denying you a whole storyline and a fight at the parents' house that nets a lot of XP. It is actually quite likely that a new player will cross these points first, as Gareth and Jonathan lie beyond the scarecrows, and that will deter many from proceeding in that direction. 2) After a certain point or a certain action, you can no longer persuade the Advocate to reveal who is summoning the Voidwoken, and thus bring on the Voidwoken fight. I haven't determined exactly what this trigger is yet - hitting a particular point on Bloodmoon Island, perhaps? - but when you're playing on tactician and every XP is precious, losing out on a whole bunch is frustrating.
I wouldn't be here griping if I didn't otherwise love the game. Over 1,000 hours logged, love the characters, the stories, the jokes. But it would be great if Larian could avoid introducing a similar mechanism into Baldur's Gate 3 (at least, maybe, hint somehow that opportunities are being passed up?).