Unfortunately, once-per-long rest features are effectively once-per-fight for players that simply spam long rest after every fight. That's a flaw in the D&D rules that has been present since the 1970s, which can only really be resolved by DMs abusing the rules to encourage players to take less long rests.
You can only long rest once per day, and the way that Baldur's Gate 3 handles this is that a long rest "advances" to the next day. This does have an impact on some quests which resolve differently (usually negatively) because you took too long.
Once I realised this I found that discouraged me a great deal from long resting, even though I think it's quite permissive (maybe three long rests before a quest advances on its own) so I made much more use of short rests, tried to save up spells or made a lot of use of scrolls to save on spell slots.
