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