A lot of these aren't exactly "niche", but afaik none of them exist on lemmy yet

Edit: for some reason, a bunch of these that actually do exist weren't showing up in search unless I specifically searched for "!community@instance". I've gone back through and added links to them here.

r/actuallesbians
~~r/anarchychess~~ !anarchychess@sopuli.xyz
r/anime_irl
~~r/animemes~~ !animemes@lemmy.ml
r/beyblade
r/bropill
r/conlangs
~~r/datahoarder~~ !datahoarder@lemmy.ml
r/ddlc
~~r/egg_irl~~ !egg_irl@lemmy.ml
r/femboymemes
~~r/forbiddensnacks~~ !forbiddensnacks@lemmy.ml
r/gravityfalls
r/heraldry
r/heraldrycirclejerk
r/infinitytrain
r/katawashoujo
r/leopardsatemyface
r/logh
r/lycorisrecoil
r/madeinabyss
r/madokamagica
~~r/math~~ !math@lemmy.ml
r/mathmemes
r/mbtimemes
~~r/mechanicalkeyboards~~ !mechanicalkeyboards@lemmy.ml
r/mushokutensei
r/musictheory
r/nails
r/nextfuckinglevel
~~r/oshinoko~~ !oshi_no_ko@lemmy.ml
~~r/philosophy~~ !philosophy@lemmy.ml !philosophy@mander.xyz
r/photoshopbattles
r/playstupidgames
r/pokemongo
~~r/portal~~ !portal@lemmy.ml
r/princessesofpower
~~r/programmerhumor~~ !programmerhumor@lemmy.ml
r/shitduolingosays
r/shitpostcrusaders
r/stardustcrusaders
r/stevenuniverse
~~r/swordartonline~~ !swordartonline@lemmy.ml
~~r/talesfromtechsupport~~ !talesfromtechsupport@compuverse.uk
r/the10thdentist
~~r/thinkpad~~ !thinkpad@lemmy.ml
~~r/tokipona~~ !toki_pona@lemmy.ml
r/touchfluffytail
~~r/traaaaaaannnnnnnnnns~~ !traaaaaaannnnnnnnnns@lemmy.ca
r/transadorable
r/transprogrammer
~~r/transhumanism~~ !transhumanism@lemmy.ml
r/transtrans
~~r/visualnovels~~ !visualnovel@lemmy.ml !visualnovels@lemmy.comfysnug.space
r/wholesomeyuri
r/yurimemes

A couple, I think. WoTshow is one I really liked. And exatheist is a tiny sub where a bunch of people who were once atheists of all different religions talk religious philosophy.

I really enjoy r/archery hope they make it here

Waiting on r/linuxmasterrace tbh

r/mbti 16 mbtis

r/infp

Hobbydrama It was kinda interesting hearing about the inner workings and happenings in hobby's you never even heard about.

r/kamenrider, r/supersentai or any of the tokusatsu subs for that matter

This seems way too unlikely to happen, but r/askhistorians. It's an exceptionally well moderated (if a bit overzealous) community that allows for both the average person to ask seemingly impossible, very specific questions as well as academics to express their knowledge and passion for those very same super specific topics they find fascinating; but have difficulty finding an audience to listen to them in their day to day lives.

r/piracy

r/electronics

r/rce

r/diy

r/diyaudio

r/diwhy

r/edm

r/edmproduction

r/angryupvote

r/masterhacker

r/mathmemes

r/sciencememes

r/physicsmemes

r/chemsitrymemes

r/bilogymemes

r/onejob

r/outoftheloop

r/printers

r/redneckengineering

r/torrents

r/tvtoohigh

r/winehq

r/youtubedl

r/weird

r/ultralight, r/myog and r/wildernessbackpacking

You can tell what I'm into.

Just the really small ones i was subscribed to, Tasker will probably be my most missed one, hard to find another forum specifically for one app!

r/ubiquiti

r/HobbyDrama or a more hobby oriented history community. Also r/AskHistorians or similar, although that one will take more effort and setting up than simply making the community. I personally use Reddit to see a couple memes and then read both of the subs I mentioned. I like seeing people who are passionate about a thing talk about the history of that thing.

some of the more or less interesting ones i came across...

r/InternetIsBeautiful r/AlpineLinux r/CoOpGaming r/antiXLinux r/devuan r/gamedeals r/privacyhardware r/opensourcegames r/FreeGaming r/fossdroid r/linux4noobs r/commandline r/channelsofyoutube r/DeepIntoYouTube r/ChannelWatch r/EatCheapAndHealthy r/Foodforthought r/initFreedom r/irc r/KeepOurNetFree r/linux_devices r/suckless r/techsupport r/unknownvideos r/usenet r/youtubeclassics r/suggestmeabook r/thinkpad r/DistroTube r/odysee r/lbry r/peertube r/FOSSPhotography r/DepthHub r/TrueFilm r/socialscience r/AskSocialScience r/UpliftingNews r/LinuxPhones r/startpages r/terminal_porn r/nodrm r/Antifeatures r/FreeAudio r/listentothis (separated by genre)

I'll definitely miss r/framework the most, the community on the subreddit is awesome

A VR (virtual reality) focused community would be nice, it has a very strong community across devices all things considered.

Eurovision is probably the one I'll miss the most from Reddit. The people I talked to their were real chill.

r/Aviation and r/KerbalSpaceProgram equivalents would be welcomed by me.

r/buttcoin, every time I feel bad about myself I like reading about crypto fails to remind myself that I could have made even worse decisions.
r/noncredibledefense, makes the horror of the war not far from me a bit more bearable

r/woodworking would be nice.

r/grandorder Probably my most used subreddit. Also r/hololive and r/nijisanji

Actually a few, but to list some

~~r/PublicDomain~~

r/MirrorsEdgeAesthetics

~~r/MovieSuggestions~~

~~r/LostMedia~~

~~rMediumReadings~~

~~r/RockinTheClassics~~

~~r/REgames ~~

r/CarHacking could also be good

Maybe~~ r/iwatchedanoldmovie ~~ Some game specifics sub's like r/MetalGearSolid, r/MetalSlug and r/HalfLife, r/moddergearsolid is a particularly obscure one.

Most of the console modding subs like r/360hacks, r/WiiUHacks which is going dark, r/PS3Homebrew and so on.

From my own feed that's about it, with the exception of some piracy ones like rCemuPiracy r/LinuxCrackSupport and r/SteamDeckPirates, among others. And a couple in particular that push a bit closer to the work unsafe side, so those wouldn't be here.

/r/futurama
/r/3Dprinting
/r/swift.

Oh boy , it will be fun when 2westerneuropean4you gets here

If anyone is looking, I made !amateur_radio (https://sh.itjust.works/c/amateur_radio).

/r/sorceryofthespectacle, /r/theoryofpropaganda, /r/darkgnosis, /r/hermeticism, /r/alternativehistory

I’d love to see stuff related to linux tech I use and obscure video game discussions. Some of my favs were:

bspwm oxenfree edgerunners

And quite a few others, but those are off the top of my head atm.