Look, there's thing out there where people will judge a work by whether they perceive it to be "character-based" or "plot-based".
And I'm not even saying these things don't exist. Some stories genuinely are only really concerned about the interesting events, and some barely have anything happen because it's all about the development of these interesting people.
But most stories don't fall into such extremes. And also, neither category is inherently "better" or more "worthy" than the other, regardless of what some book snobs will tell you. (And I say this as someone largely unconcerned, as a reader, with plot.)
Realistically, though, most good stories have an engaging plot and interesting characters who develop as a result of that plot. So which comes first: the chicken, or the egg?
See, here's the thing: it doesn't matter.
Seriously, it doesn't. When done correctly, no one ought to be able to tell which you (the writer) began with.
My own stories tend to begin with "concepts" rather than either one of the above, but for the sake of argument, let me give an example of beginning with the story.
(And, yes, my example assumes the writer is an outliner first. This doesn't matter either - whether you shape the story perfectly beforehand, during, or after the fact, makes no difference. But I have to choose one of the options for my example.)
Let's say that you invent a plot idea about a far-off world where a slave class is made up of people born with blonde hair. (I'm not saying this is a great idea - I'm not gonna throw those away on a blog post!) The plot would be about an uprising of these blonde chattels against their dark-haired oppressors.
Decent start. But then you have to decide who these people are. And if you're doing it "right" (I hesitate to use "right" and "wrong" but here I go anyway) then your characters will be chosen in such a way that their defining details suit the plot.
That is to say, your characters' personas are designed to facilitate the plot. You want someone who begins this uprising, so they need to be a character with an innate sense of pride that cannot be crushed by the prevailing attitude of both the masters and their fellow slaves.
You probably also want a major character who is more submissive - maybe you want them to work against the main character, maybe you want them to be talked around. Either way, the characteristics of this person will suit the needs of the plot.
Everything about the unfolding of this plot will depend on the nature of the characters, and their story of progression will be what drives the main plotline. Ideally, you want the plot and the story (the development of your characters) to be one and the same. To unfold together, thematically tied.
So that's one way of doing it. The other?
Let's suppose you have imagined a character who you believe is a proud human being despite oppressive circumstances. You want a figure with certain characteristics of untapped leadership potential, someone with strong beliefs that will thrive under challenge.
Okay, you have an interesting character there. But if the plot is merely about a barista who is sick of their day-to-day grind, this may not fit the potential of your character. All of that beautiful and noble design work you put into the personality is untapped.
So no, instead you realize that this person needs to be downtrodden, perhaps a slave. Maybe part of a race of slaves. And to bring out the unfair nature of this oppression, you want to highlight how arbitrary this enslavement is.
What if they live on a world where all children born blonde are considered inferior, property of the state? This will emphasize the unfair nature of the situation, and further facilitate the readers' engagement in the character's growth.
You see where I'm going, right?
Both approaches result in an identical end product. Because both plot and character should be telling the same story. Whichever was conceived of first, when developed (through planning, through the act of writing, through rewriting) they should be inseparable. The characters suit the plot; the plot suits the characters.
Inventing a plot first doesn't mean a tale with pointless characters. And creating the characters first needn't result in a work without an exciting plot.
The two ought to be entwined, so reliant on the other that in the end no reader can tell which was conceived of before the other. That's when you know that you have succeeded at writing the story.