As others have said, 5e is the most new-player friendly system they've ever released - it's quick to pick up, intuitive, well explained using natural language that is nevertheless precise in its meanings where it needs to be, and is generally the most approachable D&D system ever... there's a reason its' seen a surge in game popularity, spread and exposure, and has become at this point the longest running and most successful edition of D&D to date; you don't need to read a huge amount of books or develop a fine-tuned catalogue of rules just to play and enjoy.
That said, to be honest, being largely unfamiliar with 5e may actually be helpful to you playing this game - it will save you all the many times you might otherwise expect something to work a certain way, or a rule to be in place when it isn't, etc., BG3 is only vaguely derivative of the 5e ruleset, and it doesn't explain itself very well on top of that (this has been getting better, but it's still not great). If you go in expecting solid 5e, you'll find yourself tripping over things and making a lot of unintended mistakes initially when things don't work as they should. you'll probably do better, as a new player, just taking the game as it is, and not thinking about it as a 5e game, because realistically it's not - just learn what the game gives you instead and you'll likely have a lot of fun.
