[2][3] Her newly found success attracted the attention of stalkers: in 2019, the address of her family home in Los Angeles leaked online, causing three fans to show up at her house one day.

[4] That same year, a man was arrested for trespassing after appearing outside Eilish's residence seven times while "showing erratic behavior", such as by waiting for her by the front porch when told by her father that she was not home yet.

[24] In Eilish's concert film, Happier Than Ever: A Love Letter to Los Angeles (2021), she said that the track talks about different situations, it goes "all around the place", and it is open to interpretation.

[31][38][15][41] The song later features "weird plucky" guitar,[29][42] "eerie" piano line,[43][44] atmospheric synths, sub-bass,[45] an electro Auto Tune,[46] "hypnotic" couplets and refrains,[47] and Eilish's doubled whispery vocals[45] in a "sparse, chiming production".

[53][54] "NDA" has been labeled as "claustrophobic", "jittery", "prowling", "razor-sharp", "syncopated", and "thumping" by music commentary,[59] with Allison Stewart from The Washington Post describing it as "twitchy club [track]".

[60] Tyler Golsen of Far Out stated that the song is a "stark and shadowy version of electro-pop" and is "closer to goth-pop" than the previous single "Lost Cause" (2021), but noted how "stylistically it stays in the same sonic sandbox".

[51] "NDA" has been compared by critics to her debut studio album When We All Fall Asleep, Where Do We Go?,[62] and to the work of artists such as progressive rapper Kanye West, industrial rock band Nine Inch Nails, and hip hop and dance producer Timbaland.

[63][64][65] Sophie Walker of The Forty-Five opined that strings of this track are influenced by the Eastern music, and they with the "ticking metronome" create a "disorientating, otherworldly sound".

[45] NME's Rhian Daly wrote that the song "moves between sparse, hypnotic verses and big refrains anchored by a heavy sub bass".

[50] Bardají said that the song contains an interesting contrast with its production choices, "catchy and boastful melody", and "Billie's voice in the foreground but subjected to the habitual virguerias".

[37] Walker said that the auto tune effect put on Eilish's voice "brings this glacial, nocturnal and spectacularly odd track to life.

[45][42] Eilish starts the song by offering a reminder of the stalking incident from 2020: "Had to save my money for security / Got a stalker walkin' up and down the street / Says he's Satan and he'd like to meet.

[79] In an article published by Pinkvilla, a writer suggested that the song seemingly also talks about trust,[80] while Young Hollywood's Rebecca Breitfeller stated it is about "that life is moving too fast and too many things are coming at [Eilish] from all angles".

"[41] Gigwise's Vicky Greer deemed Eilish to be "returning to the darker alt-pop" with "NDA",[32] similarly to how Roberts opined that the song further tapped into Billie's experimental vein.

[38] Chris Willman from Variety felt the single "seems more like an offbeat album track" and it is "good to get her more unnerving side back, in full, uneasy bloom".

[84] Robin Murray from Clash said that it is "delicately composed";[85] while Sarah El-Mahmoud of CinemaBlend called the song "brooding" and "well orchestrated" with "intense back beat", as well as labeling the subject matter "interesting", however admitting that it did not "blow [her] mind".

[86] "NDA" was praised by respective editors of The Wall Street Journal and Hollywood.com, with Mark Richardson commenting "[Eilish's] hushed voice and muted phrasing need the contrast these grittier and noisier tracks provide";[68] while Sam Persall said that it is a "perfect accompaniment to the previously released Happier Than Ever singles" because of its diverse lyrics.

[29] At Chorus.fm, Adam Grundy highlighted Finneas production skills in "NDA", saying that they improved since the last projects he has been involved; while Aaron Mook suggested that the song is a good mixture of Eilish's first studio album with "something new".

While giving praise to the guitars placed in the song's pre-chorus, she found its release as a single a "mistake", explaining, "If you're going to prerelease a sizable chunk of your album, you better make sure it doesn't sound like well-worn terrain, or an obstacle on the way to shinier toys."

[93] Jackson Langford of MTV Australia put "NDA" on the third place of his list compiling of every Eilish songs, where he wrote that even though the track is not relatable, it "doesn't alienate."

He also compared it to previous Happier Than Ever singles, "My Future" (2020) and "Your Power", saying that unlike those "NDA" is an "all-out onslaught of fiery emotion as she reckons with fame's intense repercussions.

[66] On Rolling Stone-published ranking of the singer's 20 best songs, "NDA" was put on number 16, with Dolan opining that it is the "tensely humming track, with its water-torture string plucks and meat-cleaver snare thwumps, amps up the sense of claustrophobic desperation, as Eilish's bleary voice tries to break through, hungering for the freedom she's earned and deserves.

"[41] Writing for Uproxx, Rachel Brodsky placed the track on number 19 of all Eilish songs ranked, where she added that "[l]istening to the pulsating 'NDA' is even a little stressful, but it’s probably nothing compared to what its author experiences on a daily basis.

"[96] Similarly to two previous Happier Than Ever singles, "NDA" achieved moderate commercial success, which have not meet some fans expectations, resulting in calling it her "flop era".

[20] It resulted in the song's placement in the top 40 on the Billboard Hot 100, as the fifth consecutive single of the album to do so;[102] "NDA" debuted and peaked at number 39 on a chart issue July 24.

[81] Nicholas Rice of People called the visual "moody",[128] while Ruth Samuel from the Los Angeles Times labeled it "eerie", adding "engulfed in clouds of smoke as dozens of cars race past her, Billie Eilish puts a literal spin on life".

[132] Besides calling it "dark", Breitfeller said the video "particular[ly] feels very honest and emotional", and that the cars featured in it are not only a "wonderful metaphor", but also "visually extremely entertaining".

[137] On August 5, 2021, Eilish performed a five-song in BBC Radio 1's Live Lounge that included "NDA", alongside other album tracks and a cover of Frances Langford's "I'm in the Mood for Love".

[138][139][140] Next month, the singer released her concert film entitled Happier Than Ever: A Love Letter to Los Angeles, which featured a performance of the song.

[142][143][144] In 2022, Eilish embarked on a world tour that started on February 3, 2022, in New Orleans at Smoothie King Center and finished on September 30, 2022, at Perth Arena, in support of Happier Than Ever, where she performed "NDA" after "I Didn't Change My Number", before she transitioned into "Therefore I Am".