You can get a 'happy' ending in the first minutes of Baldur's Gate 3, sort of
I love a game that allows us to defy the expectations games put on us. In Far Cry 5, for example, you can wait around doing nothing at the start of the game to avoid all of the other events in the game, rolling credits without making a move. And in Baldur's Gate 3, you can make a choice very near the start that ends the adventure before it's really begun—and your character is completely happy about it.
The credits don't roll when you make this choice, so it's not really an official ending, but you do get a "Game Over" screen which either sends you back to the main menu, or to a previous load. Don't read on if you don't want to know what I'm talking about, but it's just a quick gag that can happen right after the introduction on the nautiloid.
As you wander the nautiloid crash site, you'll encounter a still-living mind flayer, and can enter into silent dialogue with it. If you pass an Intelligence check, you can concentrate on its thoughts while it attempts to manipulate you. This only increases your connection, allowing the mind flayer to telepathically suggest that you sacrifice your body to it so that it may survive.
You're given two more opportunities to resist the mind flayer's pull with Wisdom checks, but if you ignore them and choose to "lean in, as for a kiss" and then insist that "everything is fine," you hear one final line from the narrator: "Warm, wet tentacles wrap themselves around your head, and for the first time in your life, you're perfectly happy."
Even if you have living party members, the next thing you see is a Game Over screen. "Your party has been defeated," it reads.
It would be very hard to fail both of the DC5 Wisdom checks that resist the mind flayer, but I already know of two very unlucky people who had their mind flayed after passing the Intelligence check and then rolling two terrible Wisdom checks. Two!
It may not be "an ending" in the traditional sense, but it's a way to end the game, technically, and the protagonist is happy—albeit briefly—so that's enough for me to claim I've beaten Baldur's Gate 3. Now to spend the rest of the weekend in my main campaign (where I did not let a mind flayer devour my brain) wandering around talking to animals instead of advancing the plot.