As a person w/ out d&d experience, who was broadly aware of the game (ie. know classes but not the difference between actions & bonus actions), I didn't have a terrible time onboarding. I started as a paladin and found that most of what I could do was pretty apparent and my friends who probably knew less than me seemed to catch on just as fast.
Some things like throwing potions wasn't as obvious but I could see some choice paralysis from being a spellcaster.
Honestly after a while I stopped caring and just enjoyed that I could do three actions per round as a Monk. Does it matter that Gale can't throw this grenade? Nope. Can he take this healing pot? He sure can! I don't care for minmaxing and optimising my playstyle, I prefer to wing it and see how it goes. If an NPC dies in the process, RNGesus has spoken.
I know this will be a very controversial comment, but I actually can't stand the combat (extremely unfamiliar with the genre as a whole, and I've also never been a fan of turn-based systems), but love the game to death. As a result, I'm using a trainer to essentially trivialize combat encounters, because my BG3 addiction stems from the characters, their stories, the incredible world and the exploration it offers, the side quests, the lore, the insane detail in every corner of the map. I also work 80 hour weeks and want to spend the little time I get with the game doing what I love most, which is exploration and delving into my characters' stories.
I've just gotten through Moonrise Towers (and have done all I can find to do in each area so far, although I already know I'll be doing multiple playthroughs), and it's one of the most immersive and enjoyable gaming experiences I've ever had, despite the fact I'm quite literally cheating my way through combat encounters. I'm basically playing it as a very interactive 'choose your own adventure' novel, with weapon and armor pickups being cosmetic-only in nature, and the focus of my playthrough being on exploring the world and delving into its inhabitants' backstories and the mysteries they hold.
40 hours later of couch co-op with my inexperienced partner who chose Wizard for some reason, and their character is finally useful in battle near the end of act 2.
I try not to control them, I just say what I'm doing and planning so they don't launch my team off a cliff. Occasionally I'll say "Yes, counterspell cloudkill please." but I'm mostly hands off. When asked for advice I give it, I'm not a monster, I just think if we're playing together we should both get to play.
I haven't played any DnD since 3rd, and my partner loves these role playing shows like Critical Role or whatever. My biggest takeaway I've had from our sessions is that those shows most not have any mechanics whatsoever.
DnD is stupidly complicated and hopefully this is a call out to WotC to realise that their system isn't the gold standard because of its rules, but moreso out of happenstance.
I only ever found the magic classes complicated when I was new. The limited spells per day and number of cast rules, what you had access to as what, memorizing, etc... All a lot of work compared to other games I was used to just having a mana pool.
I just turned it down to the lowest difficulty setting until I learned how the system works. By level 7 I'm holding my own in balanced setting and enjoying the hell out of this game. It's all I play now lol
There's a fair bit of onboarding and constant learning if people are coming into D&D or similar games. I felt the same with pathfinder trying to understand spell metamagic (caster levels, DCs etc)
That’s odd because I’ve always struggled to grasp the entire rules of D&D in a whole for playing any sessions. But BG3 has managed to present all these elements in such an intuitive way I now feel like I finally have a great grasp of all the rules. I’ve even found I have to start playing on tactician difficulty and whilst dressing my party in funny outfits and ignoring armour buffs, or I’m starting to find the combat too easy once you start to get creative.