I would define BG3 as open world, but not sandbox. A sandbox game requires sandbox gameplay, which BG3 lacks. Sure, it's less linear than Solasta (which is literally a one-track railroad as far as I've seen). Going around "mining" crystals in the open world isn't any more sandboxy than going around "mining" pots for rupies in an old Zelda game.

Compare with say, the Witcher games. The first two are pseudo-open, half-linear games but not very sandboxy. In Witcher 3, which I still would not define as a fully sandbox game, they increased the sandbox elements to a level where you could actually roam around and be somewhat of a witcher doing witcher stuff, if you wanted to. In comparison, BG3 is more akin to the first two games. And you could run around and pick flowers (ie, mine) all you wanted in those games too, and even use those flowers to craft things. But it's not really sandbox gameplay, is it?

You yourself mention Skyrim as an example, which yeah, that barely passes the bar for a sandbox dungeon delving game I guess. But isn't the major differences between that and BG3 self-explicit? Skyrim is more open world, more built to just take off in a random direction and find something to do, less linear in its presentation (but actually more linear in it's quest structure, because Beth can't write nonlinearly for shit -- just watch me go off on a tirade about the Windhelm murder mystery quest here, I'll do it, I'm warning you).

For BG3 to be sandbox there'd have to be some kind of sandbox gameplay or interactions, but there's not. I'd compare to the GTA games -- all of them are open world, yet none of them are as much sandbox as San Andreas, where you interact with the open world in a more sandboxy manner.

Which kinda leads me into what "sandboxy" means: to me, the core of the sandbox concept is a player-driven, non-structured gameplay loop, where goals are either set by the player themself or emergent from the gameplay itself. BG3, as a heavily plot driven game, dies not meet these criteria. As I see it, BG3 is no more sandbox than the original two BG games were, which are (while, again, kinda non-linear) decidedly not sandbox games.

Optimistically Apocalyptic