Quest logs, mission trackers, etc - specifically the tracking and displaying of player progress of storylines that may feature branches or alternate outcomes, all in the same world, but the journal itself not necessarily diagetic in nature. Not simply mission trackers/waypoint markers w/ text, but the actual recount of your progress. Some fun thoughts below the cut, and a question for those interested in the topic!
I don't really think I've ever seen it done masterfully; at best, I don't remember because it was either not heavily required, or so mid as to be unnoticed good or ill, at worst, sometimes not-present is better than 'factually wrong' or 'almost antagonistically unhelpful'.
The biggest flaw I see isn't even in UI. It's in, I suppose, what I'd say is UX: journal entries are rarely, if ever, sufficiently written, in all senses of the term. Whether it's because there's not enough stages of them, or because they're not shown to you in their entirety, or because there's not an alternate 'completed' version of the objective text so there's no step that describes what the result of that objective was, or they're literally not providing enough information by leaving out specifics or even locations.
And I think it comes from being developed alongside everything else, b/c that's really the only way to do it if you've got a big sprawling quest-log-requiring thing. And things chop and change and get remade or taken out, and not everything gets perfectly cleaned up - all genuinely realistic things - and we end up with quest logs as they are.
For me? I want a succinct, easily acessible synopsis of the entire quest's objectives and each of their results that I've done so far, up to the current step, so I can fully remind myself of the context of what I'm doing and why. This is a huge boon for being able to return to a game after many months away, as well - it solves half of the problem (the other half being remembering how to play, and I don't think I've ever seen a game acknowledge you've been away for a long time and then offer you some light recaps because of that.)
I like diagetic journals, but never prioritized over the above; if it's not going to make sense in-world to have the journal be an object the character uses extremely regularly, then it's still fine to have it be in first/second person, again, so long as a fully detailed version is immediately accessible. Like, prominent-hotkey-when-highlighting-the-quest levels of immediate.
(Specific to BG3, if you're going to nest quests inside quests, please don't have them basically be the same quest, like for most of the Companion quests. I get that some come and go, but Larian isn't very strict about keeping the text/entries for each selectable 'quest' - the top-level quest and its sub-quest - cleanly separated and updated. It's just not well organised and splits info between two different areas.)
Searchable would be great, but not always useful. Comes down to platform as well, which almost all the UI does, as well.
What do you consider to be the most important element of a quest journal? Or, if not important, your favourite/most desired?