I would love to know if they plan on leaving it so you can change your prepared spells at any time (it could be a holdover from DOS), or if they plan on fixing that so it’s like D&D. It’s a bit hard to evaluate party balance during EA unless we know either way.
I found (probably linked somewhere on this forum) an old interview/stream/... in which they said something like we would only be able to prepare spells and level up at camp.
I think it was in the first interviews about the game. I hope they didn't change their mind.
Any time you are not in combat, you are out of danger, and you can go to camp/have a long rest. So any time you are not actually in combat, you can prepare spells ( and level up I guess ) by going to camp. The 5e rules themselves have no consequences for going to camp except time spent doing so ( This is just one of the inane rules that DnD has always had, and somehow never replaced with something superior ).
So, going to camp just to change spells in the BG3 videogame would be time consuming, boring and pointless, and would attract a lot of criticism. As BG3 has no concept of time, due to the co-op design ( player timelines are not synchronised ) it really makes perfect sense to allow spell preparation/level up when outside combat.
The only reason you might restrict spell preparation/level up to the long rest in BG3 is if you artificially create a hazard as a consequence of resting. In early versions of DnD ( and BG1/2 ) this was by a RNG against "wandering monster" tables. You could do that, but I don't know how popular that would be either.