When Tora Northman, 23, scrolls through Instagram, as she does multiple times a day, she often sees a picture of Gwyneth Paltrow attending the 1996 MTV Video Music Awards in a burgundy velvet Gucci trouser suit in her feed. Sometimes a friend will have posted it. Other times, it has come from one of the 1990s- and Y2K-themed pages that have proliferated online, including @90sanxiety, @90smilk, @early2000sbabes and @literally.iconic, the owner of which claims, in the account’s bio, to have been “raised by paris and britney.”

“Every single time I see her in that red velvet suit, I will ‘like’ it, and I will probably share it,” Ms. Northman said.

Gen Z’s style obsession with the 1990s and ’00s is well documented. See Olivia Rodrigo at the White House in a “Clueless”-esque Chanel suit from 1995, or Bella Hadid celebrating her birthday in the opening look from Gucci’s spring 1998 collection. Survey a gaggle of teenagers and you’ll spot “vintage” camo trousers, platform shoes, strappy tops, belly chains, slogan T-shirts (“Boys Lie!”), hibiscus-print dresses and butterfly jewelry.

On the resale platform Depop, there were 290,000 unique searches for “Y2K” in September, October and November, according to the company. (It is one of the most popular searches on the platform, a spokesman said.) Over the same period, there were 92,561 searches for “low rise jeans” and 150,133 for “Ed Hardy.”

Paparazzi shots and film stills from the period trade online as curiosities from a seemingly simpler yet more decadent time: Sarah Jessica Parker as Carrie Bradshaw, Princess Diana, Britney Spears. There is young Naomi Campbell, on the runway for Chanel, Gaultier and Versace; flashy Victoria Beckham in her past life as a pop star; Paris Hilton in a “Don’t be Jealous” T-shirt.

For those old enough to recall dancing to Prince’s “1999” at midnight in sparkly plastic sunglasses that spelled “2000,” the notion of pining for the cultural (and fashion) stars of the era of financial and technological uncertainty may be baffling.

But many of those who came after suggest that the attraction is about a lot more than simply the fun of trying on the outfits of another era, or the start of a new 20-year fashion cycle.

‘Being More in the Moment’

One of Depop’s most successful sellers, according to the company, is Isabella Vrana, 24, whose shop promises “90s & 00s gems for u angels.” She lives in London, employs three people and has sold more than 16,000 pieces to those eager to cosplay an earlier existence.

On a recent podcast, Ms. Vrana learned about the fear in the late 1990s of a “millennium bug” that could collapse worldwide infrastructure through date formatting errors. The idea that technology could fail was shocking to her. She recalled her boyfriend’s mother telling her about a time before cellphones, when, if you lost a friend during an evening out, you’d have to go home and sit by the landline.

“That just seemed so cool to me,” Ms. Vrana said. “I like the idea of people just being more in the moment.”

To crush on the past is a respite, she said, from “the things that we do a lot, but hate, like being on our phones all the time or taking 50 nearly identical photos and then obsessively checking through and finding your favorite.” (There is, of course, a vivid irony to a generation using smartphones and the internet as a portal to a less-online age in order to fantasize about limiting their reliance on technology.)

Ms. Vrana knows it wasn’t all so great way back when; that homophobia, racism and sexism were more tolerated, that many female celebrities were harassed and controlled. But still, she said, “people, to just some extent, seemed more chill.”

Much of this has to do with nostalgia for an age before social media and technological dominance, especially among young adults who have grown up documenting themselves and being documented. In the ’90s, after all, there were no bathroom selfies. No recordings of livestreams, arm outstretched holding up a device. No iPhone Note apologies. Most people didn’t seem to even touch a camera themselves; they were captured, instead, by others — living rather than posing.

James Abraham, 35, who runs the popular Instagram account @90sanxiety, which he started in 2016, sees the intrigue as related to the sense of something uncompromising about the period — the “rawness, the realness,” Mr. Abraham said. “‘Purity,’ that’s the keyword.”

‘Hot and Unbothered’

In the ’90s and aughts, Ms. Northman said, people seemed more “like themselves.” Sure, today’s celebrities perform openness through social media, but often, she noted, they are actually the opposite: strategic and controlled.

Ms. Northman loves the way celebrities appeared to dress effortlessly in the ’90s, in oversize suits with unbuttoned shirts, thong-revealing jeans, ironic T-shirts and skimpy, sparkly halters. And the way they draped themselves over new partners and smoked on the red carpet, or got drunk and said uninhibited, quippy things. It seems, she said, that everyone was “hot and unbothered.”

For her, images of, say, a teenage Kate Moss taking a drag from a cigarette provoke a strange longing for sensations and scenes she can’t quite summon but imagines she would like: evenings out without selfies; the smell of smoke in a nightclub; the sound of a friend, unanticipated and unplanned, knocking at the front door, asking you to come and hang out.

Charlotte Mitchell, a 21-year-old law student in Manchester, England, said that she imagines the ’90s and ’00s to be “like now, except social media is not a thing, so everyone is just dressing how they want to.” Last year Urban Outfitters, where she works part-time, went big on the Von Dutch revival, peddling ’00s-style tank tops and trucker hats. She bought a cute top bearing the logo, thinking it was a cool new brand. Her 30-year-old manager, disapproved, she said, scoffing, “You weren’t even born.”

A child of the 2000s, Ms. Mitchell is, understandably, woolly on the details of the age her style apes, preferring, like her peers, to picture it through the haphazard, beautiful images that trend online. As with nearly all of those interviewed, she had never heard of “Seinfeld” or “Will & Grace.” She has never watched an episode of “Friends.” “It has never appealed to me,” she said.

(Ms. Vrana disagrees. One of her style icons is early Jennifer Aniston as Rachel Green. “I love ’90s office wear,” she said.)

“My childhood was ‘Hannah Montana,’” Ms. Mitchell said. Asked if she’d heard of “The O.C.,” which premiered in 2003, she replied solemnly: “I don’t know what that is. I’m sorry.” How about the O.J. Simpson trial?

“I feel like I wouldn’t have heard of him if it wasn’t for the Kardashians,” she said.

(Another 21-year-old, Sam Fitzpatrick, who works in social media and lives in Liverpool, England, said in an interview that she did in fact appreciate wider ’90s culture and “old music, like the Spice Girls.”)

The Power of Paris

Harriet Russell, 21, wears three sparkling tooth gems, straightens her hair and buys her ’90s stuff on eBay. “It’s usually some mum clearing out her loft who doesn’t know what everything’s actually worth,” said Ms. Russell, who lives in East London. Her saved searches include D & G, Walé Adeyemi, vintage Burberry, Air Max 95 and Miss Sixty.

For a while, her friends tried to bask in the image, if not the reality, of a technology-scarce life, she said. Some bought flip phones to pose with in their smartphone selfies. Many, over the summer, fell in love with an Instagram filter that made images look as if they were taken by a primitive camera phone.

“For a while everyone was back on film,” Ms. Russell said. Now some of her friends, keen to be ahead of the curve, have moved back to digital, carrying tiny snapshot cameras when they go out at night.

“I guess that’s a ’00s thing, when no one had iPhones, and you’d take a camera out and then, like, export it on to a PC or something afterward,” she said. “I don’t know how that would even work.”

Ms. Russell said she likes channeling Paris Hilton’s rich-girl “persona.” She loves the “sunglasses in the club” look, the “designer bag, big logo,” the skin on show. To her, such fashion seems “liberating,” she said. “We need and want to be carefree.”

Indeed, the Paris Hilton of the past (she is now 40), once a bastion of playful nihilism, has become an unlikely hero to some half her age. Nicole Stark, a 19-year-old whose Depop shop, GlowNic, promises “Y2K x 90s garmz Black owned,” agreed that Ms. Hilton, a billionaire’s daughter with a persona built on blindness to her own privilege, would likely have been canceled if she had risen to prominence today. Nevertheless, Ms. Stark loves her, viewing her as a “powerful woman” who refused to conform.

To Ms. Stark and many of those interviewed, the stories of female celebrities like Ms. Hilton, who came of age in an entertainment industry dominated by men, provide models not only of outlandishness as rebellion, but also of women who were savvier than many people gave them credit for.

For many in Gen Z, Ms. Hilton, with her sparkly outfits, unbridled confidence and pouty refusal to work day jobs or capitulate to appropriateness, as immortalized in “The Simple Life,” encapsulates the freedom of the era — the humor, ease and flippancy.

“She just did whatever she wanted,” Ms. Mitchell said, almost awed. “She wasn’t influenced by anybody.”