I've a front story

My backstory is I joined this party to forget about my backstory.

Genius

I like a short backstory that provides hooks. "Disgraced son of a noble family that became a warlock when everyone expected a sorcerer" is fine.

12 pages where all the cool stuff already happened is bad. Write that as a book.

I usually write a handful of paragraphs and then never look at them again. It's mainly to get me into character and develop a feeling who this person is. Then I go play. If the DM wants to know more, I can either improv it or review what I've written.

My backstory is 12 pages, but I wrote it in very big letters and I used chalk and smudged it quite a lot

My backstory is 3 pages. I picked the noble knight background and they're my retainers.
- My backstory is one page long, I'm looking for a girl named Page, that's it, just any girl named Page.
ah, a barbarian
I tried this in first grade once. The teacher was not a fan lol

I wrote a backstory, along with what my character wants to achieve.
No one else wrote a story. Neither did the DM apparently.
He made my story the campaign, and the other characters my squires.

A really important thing that I find a lot of writers need to learn is that backstory is not character depth. You can write an incredibly deep and complex character without ever telling us anything about their past.

Depth comes from complexity. Complexity is found in contradiction. Real people don't have some simple set of programming that defines them. This is why I despise the alignment system; it's basically a textbook for creating uninteresting characters. In real life people often hold complex and contradictory (or seemingly contradictory) ideals. Or they profess one ideal but live out another.

Think about a character who lives by a philosophy of always putting themselves first. Think about all the times they do something for someone else, not even really understanding or accepting that they're breaking their own rule. Think about why they would do that. That's character depth. Maybe there's something in their past that explains why they are that way, but we don't ever need to know what it is. And in truth, most people can't be summed up as one or two pivotal events. We're the sum of every single moment in our lives, all put together in one complex mess of a human being.

The alignment system really isn’t that complex or strict. Lawful means you’re someone who generally holds to personal principles and chaotic means you go where the wind blows. Good means you do what’s best for everyone and evil means you do what’s best for yourself.
Chaotic Good would be the hardest one to wrap ones head around. That would be someone who wants to help people but isn’t really sure how. They don’t have a strong oath like a paladin and they don’t know if they should be nice everyone or if they should maybe be a little quicker to fight against the obvious bad guys.
Ultimately though, the alignment is system is something pretty well explained in the DMG, from what I remember, but with D&D people just look at poorly informed memes and then complain about how rules don’t even function in the actual book. Their ignorance is not the fault of the source material.
Otherwise I generally agree with what you’re saying. I would like to add that you can also create depth with character growth. A simple character is a fantastic starting point if you actually develop them over the campaign.

I generally make a 3 paragraph backstory. How I came to be, how I was wronged, and who wronged me.

A level 1 with more than a few bullet points of backstory doesn't make a ton of sense to me

I don't mind it being deep, just don't fill it with your actions and deeds. A big part of fun for TTRPGs is 'play away from the table', which for the players is typically making art, backstory or builds for current or future characters. Most long backstories I read don't invalidate a level 1 character but mostly explore values, just as my real life story could be as deep as I choose to write it and I'd not even have the skills to be level 1.
My suggestion is:
Get people together for a session 0. Only pitch the campaign and tone then, if not construct it collaboratively too.
Hand out pieces of paper or card face down, have each player take 1, and ensure there is one between each player. These cards say Love, ally, rival, or enemy.
Explain that players should make an NPC for their backstory that matches this word, and should make a shared NPC with the person next to them based on the card between them.
Now let them take another card of their choice. They can either make another NPC with this, or use it to make the relationship to one of their shared NPCs asymmetrical.
They can design their NPCs and backstory now or before session 1, up to them.
Finally, explore what the players can choose to do to contribute between sessions to the game. If they don't do anything, that's fine, but they should have a way to meaningful contribute to something. Typically I encourage world building and cultural lore, such as unique foods and why that has a thematic resonance.
This is hard to structure, I had a player who was a former forever DM, who played a knowledgeable librarian in a former monster hunter guild. I asked her to make some monster statblocks, as she'd know them inside and out in character.
My advice to players:
Make your backstory show that your character has done no huge deeds yet, and most importantly, have everything that matters in it revolve around NPCs. Not just is this the best drama, but NPCs can move, join factions, be redeemed, betray you, die and everything else.
That cost halfling village you design that perfectly exemplifies your character, but will never be seen in this urban campaign halfway across the continent? Make the most important part of it the mayor's daughter who happens to be your childhood friend.
The strange necklace that made you stronger but more angry when you wore it? The final time you saw it was when your brother stormed out of your co-owned business after a bitter argument.
The lord who helped you smuggle your liquor into the city? That's the same lord that wrongfully imprisoned the player character next to you.
One of my favourite scenes from a campaign came when a player, after spending a session getting the chance to meet with a resistance leader, turned to the others and said "this is my ex-wife". That whole dynamic was interesting too, as both had come from a warrior culture and initially parted due to neither being the "strong warrior", now both trying to fight against that same faction a decade later.
My all time favourite NPC was a talented tailor in an urban campaign, who owed one player character a favour and was generally fond of them all. Nothing like the party having a go to guy for fancy or silly outfit amendments.

My backstory: I am a [[class]] who is excited to go adventuring with my best buddies who I have no conflict with at all, and I am willing to die for them.

It's nice to have a few hooks and characters and things that a DM can use if the player wants them, but player interest is the key part. A character's background is there to allow for opportunities to tie the character into the world and vice versa, but you can also achieve the same thing by just giving weight to interactions and having them reverberate through the campaign.

Like, in the campaign I'm running now my players came across an ancient shrine to an axolotl-folk storm deity that was built as a sensory stone playing a ritual, with a hallowed ground spell creating a tongues area of effect. Some spiders had made a nest around it and were communing with it, but rather than talking to the spiders, they immediately shot them and lit the forest on fire. So I added a spider-folk cleric of said deity, gave them some ettercap followers, and had the surviving spiders that ran from the fight go fetch them to get their revenge. Now they've got someone extremely formidable that they have to deal with who is only there because they burned the forest around the shrine.

They weren't initially intended to be in the campaign at all, and even the shrine was initially mostly a throw-away set piece to make a bit of forest more interesting. But because there was a significant interaction there that ought to have consequences, it made sense to add more context around that location.

Letting the players determine which bits get fleshed out on the basis of which bits they show interest in or interact with gives weight and substance whether they go in with a backstory or not. Some players are going to want to load up on backstory and give the DM plenty to work with straight from the beginning, some won't. As long as you're responsive to what your players do show you they're interested in, it'll benefit your campaign when you lean into it.

meh. This is HIGHLY table dependent. Some groups want deep narrative drama. Others just wanna get high on the confiscated goods and smash goblin face

I mean really your first few levels should be your backstory. You don't have to complicate that

I have a vague concept of how they grew up around highschool-ish, but motivation is little more than “here for the vibes” lmao

You know I like my characters when they show up as "I don't have a backstory" and you get so invested in them that they end up with "I have, like, seven characters with full sheets who are all linked to this character, and a whole culture to their site of origin."

Source: Ask me about my Tabaxi (-... acutally, Tabaxi is its own plural)

Parents dead. Given up as an orphan at some church or academy (depending on class and race).

End of story!

So your character just pooped into existence without any characteristics?

Yep. Wizard did it.
The wizard wanted to fuck her, but there was some weird virgin/whore stuff going on in their head when they threw the wish spell, so she's a succubus who cannot comprehend the concept of sex-but is still entirely a succubus in drive and demeanor. She's very bad at it.