Here is a list of the NSFW (not necessarily porn) ones (use this Reddit mirror for clickable links):

1M+:

r/Amateur
r/amateurcumsluts
r/BiggerThanYouThought
r/BreedingMaterial
r/BustyPetite
r/CollegeAmateurs
r/creampies
r/cumsluts
r/CuteLittleButts
r/GirlsFinishingTheJob
r/gonewild30plus
r/gonewildaudio
r/gothsluts
r/HoldMyFeedingTube
r/holdthemoan
r/LipsThatGrip
r/milf
r/nsfw_gifs
r/nsfwhardcore
r/OnlyFans101
r/OnOff
r/palegirls
r/PornID
r/PublicFlashing
r/Pussy
r/RealGirls
r/squirting
r/TinyTits
r/worldpolitics

500k+:

r/abelladanger
r/AssholeBehindThong
r/assinthong
r/bdsm
r/bodyperfection
r/Boobies
r/Braless
r/Breeding
r/burstingout
r/DarkAngels
r/darkjokes
r/facedownassup
r/FestivalSluts
r/Fingering
r/FlashingGirls
r/GirlswithGlasses
r/GoneMild
r/GoneWildStories
r/gwpublic
r/horny
r/Hotchickswithtattoos
r/hugeboobs
r/IndianBabes
r/obsf
r/OnlyFansAsstastic
r/orgasms
r/PantiesToTheSide
r/PLASTT
r/PornStarletHQ
r/Ratemypussy
r/rearpussy
r/RileyReid
r/seduction
r/seethru
r/SexyTummies
r/shavedpussies
r/simps
r/slutwife
r/StraightGirlsPlaying
r/Tgirls
r/thighhighs
r/tits
r/traphentai
r/whooties
r/WomenOfColor
r/YoungGirlsGoneWild

250k+:

r/adultneeds
r/AsianAmericanPorn
r/bootyshorts
r/BreakingTheSeal
r/BreastEnvy
r/broslikeus
r/cameltoe
r/collegensfw
r/Couplesporn
r/CuteModeSlutMode
r/datgap
r/doublepenetration
r/ExhibitionistSex
r/FemboyHentai
r/fuckingmachines
r/GirlsWithGirls
r/GoneWildSmiles
r/hipcleavage
r/Ifyouhadtopickone
r/LatinasGW
r/legs
r/lewdgames
r/naughtyinpublic
r/Nofans
r/OnlyFansBusty
r/OnlyFansPetite
r/outercourse
r/PAWGtastic
r/pelfie
r/phgonewild
r/SexyFrex
r/slightcellulite
r/spreading
r/suctiondildos
r/tight_shorts
r/Titties
r/WeddingRingsShowing
r/westernhentai
r/WholesomeHentai

100k+:

r/3DHentai
r/analcreampies
r/Artistic_Hentai
r/AttackOnTitties
r/AussieGirls
r/Beardsandboners
r/bikinibridge
r/Bustyfit
r/celebritymommy
r/Clits
r/DadsGoneWild
r/EdgingTalk
r/Emily_Lynne
r/fetish
r/FutaCum
r/futanari_comics
r/GirlsWithToys
r/handinpanties
r/hotwifechallenges
r/JerkOffToAnime
r/lickingdick
r/Mooning
r/netorare
r/nopanties
r/NSFWfashion
r/Oilpen
r/OnlyFansBlonde
r/OnlyFansBrunette
r/Onlyfanssmallgirls
r/Paizuri
r/Perky
r/PornstarsHD
r/promoteonlyfans
r/realsexyselfies
r/RiskyPorn
r/sexygirlsinjeans
r/SiriPornstar
r/SissyChastity
r/softies
r/solesandholes
r/spanking
r/spidergwen_34
r/TheUnderboob
r/TheUnderbun
r/Thighs
r/ZootopiaPorn

50k+:

r/AirplaneNudes
r/AltBoobWorld
r/animalcrossingr34
r/chickswearingchucks
r/dadbod
r/Daddypics
r/DarkSidePlayground
r/EdgeTogether
r/FootjobCum
r/FootTalk
r/gingerdudes
r/GWASapphic
r/HeSquats
r/HorrorMovieNudes
r/LadiesInLeather
r/LuckyPierre
r/naturalpenis
r/NoFansCouples
r/OnlyFans101BrandNew
r/OnlyFans101Inked
r/OnlyFansNaturallyHot
r/OnlyFansReds
r/OnlyFansSHMILFS
r/Oviposition
r/r4rindia
r/SensualMFM
r/sextstories
r/sportsbrasGW
r/Stunners
r/uncut_cock
r/VentiHentai
r/yaoigif
r/yurigif

50k-:

r/032r4r
r/3Dfurs
r/AAPWMOB
r/ageingpunks
r/AhMenOfCulture
r/AITentai
r/AltPussyWorld
r/AngelinaMichelle
r/AnimeMILFS_AI
r/ankletporn
r/Artistic_Ecchi
r/AsianCleavage
r/AussieCouples
r/AussieDudes
r/AzurLaneEcchiHentai
r/BDSMNot4Newbies
r/BeardPorn
r/beasissy
r/beautevil
r/BellinghamExhibits
r/BigEars
r/bigsoftcock
r/BlackGoddesses
r/blackmale
r/bluelingerie
r/Boob_Holes
r/BrOnlyFans
r/bullypie
r/CelebFapClub
r/CelebSizeQueensReturn
r/chastitysnook
r/Cheetahfurs
r/chubbypuss
r/ChurchOfAkane
r/ChurchOfRikka
r/CLTgonewild
r/Cuteyiff
r/daddybears
r/DegreesOfLewdity
r/DesiGoneWild
r/DFWents
r/differentspecies
r/dirtymitten
r/DirtyWritingPrompts
r/disturbingmovies
r/DoeHoes
r/DragonYiff
r/embarrassedyiff
r/emmapaisley
r/EscapistPorn
r/escortclientsonly
r/EspeonNSFW
r/FeetTouching
r/Female_Yiff
r/fitfurs
r/FlareonNSFW
r/Fluttershy_NSFW
r/FootWorship
r/furrybdsm
r/furrylingerie
r/FutaSub
r/GenshinBondage
r/gfdpersonals
r/Gfurcomics
r/Girls_With_Pitchforks
r/girlsinhoods
r/GlaceonNSFW
r/gonewanton
r/gonewildpopping
r/Grandpasgonewild
r/GunYiff
r/Hayasaka_NSFW
r/Hentai_DPs
r/HeterosexualYiff
r/hifirushrule34
r/HighEndEscorts
r/HugeToys
r/Inzestdoujinshi
r/JeffreyDahmer
r/JolteonNSFW
r/kasumi
r/KorraNSFW
r/KrystalNSFW
r/LansingSex
r/LeafeonNSFW
r/leglocking
r/marriedsex
r/MensSwimsuitChallenge
r/MommyCock
r/MSC_irl
r/MSC_yiff
r/neutered
r/newjerseyents
r/NippleClampGirls
r/NoFansMild
r/NSFWarframe
r/NSFWmobilewallpapers
r/OldDicks
r/OnlyFans101Asstastic
r/OnlyFans101BabyDolls
r/OnlyFans101Badremoved
r/OnlyFans101BustyBabes
r/OnlyFans101Ebony
r/OnlyFans101FitGirls
r/OnlyFans101HotMomBods
r/OnlyFans101Mouthfuls
r/OnlyFans101TallGirls
r/OnlyFansAPAC
r/OnlyFansEasternEurope
r/OnlyFansFaces
r/OnlyFansFashionistas
r/OnlyFansFootLovers
r/OnlyFansJustRight
r/OnlyFansNerdyGirls
r/OnlyFansNeverNude
r/OnlyFansRainbowHeads
r/PaigeNo
r/r4rasian
r/r4rfurry
r/RealBDSM
r/ReturnofPickOne
r/RockyEmerson
r/scamlinks
r/selfsuckfur
r/Simulingus
r/SmallButts
r/stackonmyrack
r/StomachDownFeetUp
r/suckinginformation
r/SylveonNSFW
r/TheRangoonMother
r/TigerYiff
r/Tinkerbang
r/tinygirlslargeshirts
r/TraaNSFW
r/TribalYiff
r/UlmGonewild
r/UmbreonNSFW
r/vegansgonewild
r/VolcanoVaporiser
r/wetspotguys
r/WhitePantiesBlackHose
r/whitetopsblack
r/wholesomemonstergirls
r/WindowBeauty
r/yiff_irl
r/yiff69
r/Yiffbondage
r/yiffcrossdressing
r/YiffgifsOnly

Good. There are lists of NSFW subreddits so you can find the intersect between the two lists, or you could use the GNU utility curl to query each of the subreddits on old.reddit.com/r/<insert_subreddit_name>, use grep to isolate responses that redirected to https://old.reddit.com/over18?dest=https%3A%2F%2Fold.reddit.com%2Fr%2F<insert_subreddit_name> and then the sed command to extract subreddit names only.

Edit: Did just that; see my other comment or Reddit mirror for results