Dungeon Meishi for a recent one.

Otherwise my pick is Full Metal Alchemist: Brotherhood (my favorite anime/manga)

Since this is being asked on Hexbear and not r/manga, I'd recommend "Sensou wa Onna no Kao wo Shiteinai," the manga adaptation of Alexievich's "The Unwomanly Face of War." That book is a collection of interviews with female soldiers of the Red Army that fought in the Eastern Front of WWII. As with all things USSR that see the light of day in the English speaking world, the author is an anti-communist, which is why she won the Nobel Prize for Literature for this book. However, the work is still worth reading because the interviewees are all Soviet war heroes and their deeply personal stories are the focus. Alexievich's "capital T Truth" fetishist shtick means that she doesn't often editorialize or interject, for example, every time Stalin is mentioned with "By the way, dear reader, remember that he ate all the grain" like Western accounts of socialist history do (though there are a billion footnotes crammed in the book version that "clarify" the interviewees' narratives with the anticommunist correct-think "fact checks"). The illustrations really bring to life the stories of the interviewees in a vivid way and so it's worth checking out.

Some great historical fiction include "A Bride's Story," set in 19th century Central and West Asia, with a great cultural anthropology-lite style narrative, and "Song of the Long March," which is set in Tang China and has a great portrayal of the deeply interwoven relationships between Han Chinese and Uyghurs in that historical period. I actually came across that work before all the Western atrocity propaganda started clogging the airwaves in the late 2010s and I'm personal grateful to it for pre-emptively being my first impression to the Uyghur Chinese people rather than having some shoddy copycat Holodomor 2.0 plagiarized slop become the introduction to that culture.

As a purely personal aside favorite, I'd also recommend "Fire Punch." It has a lot of the typical anime genre nonsense and really, the only reason I'd recommend it is that it has one of the best portrayals of an LGBT character in manga and anime. I was deeply struck by it personally and I've also seen heteronormative responses to the manga remark that the character humanized "LGBT individuals" as something beyond a "concept" for them.

Land of the lustrous

Jojo's Bizarre Adventure is my personal favorite.

I really liked BLAME! if you like cold, alien anime about people in a decaying concrete world.

Edit: manga* I don't know why I said anime. Got anime on the brain (always).

Monster is pretty good and Pluto both by the same mangaka as 20th century boys, my favorite ongoing manga is Chainsawman which is a bit of a shonene but it has no high school stuff in part 1.

Obligatory "Goodnight Punpun" recommendation. Also, the original Akira manga is a masterpiece, the movie doesn't do it justice (even though it's still pretty good).

Let's see, I'll just go through my ComicRack library and see what I'd actually recommend...

For non-highschool yuri manga:

• How Do We Relationship, which is great and was something someone on here recommended to me in the first place. It's both sweet and soul crushing at times, and seems to finally be heading towards a conclusion after 122 chapters. Horny, but in a subdued and very queer way.
• Octave is very similar, but much shorter. Slightly horny, also in a queer way.
• Catch These Hands is a very short, very dumb story about a couple of former delinquents starting to date for contrived reasons, both of whom may actually be ace for how completely and utterly not horny at all this is.

Non-yuri manga:

• Dungeon Meshi starts off strong and has a lot of neat worldbuilding, but starts going downhill around volume 5 and jumps the shark somewhere around volume 10 or 11 in a way that completely ruins all the cool worldbuilding and earlier themes. Still recommend it, though. Not horny at all.
• Akumetsu is basically "what if Death Note was about Deadpool instead a whiny fascist dipshit and also it was specifically about that knockoff Deadpool killing expies of actual Japanese politicians over their corruption scandals?" and although I've only gotten through 5 of its 18 volumes so far it's pretty decent if politically incoherent. Not particularly horny, just some gross Eyes Wide Shut stuff in the beginning.
• ZOM 100: Bucket List of the Dead is amazing and manages to be a hopeful, class-conscious, pro-social zombie story about a couple of burnt out wage slaves setting out to do everything they'd never gotten to do because they were too busy working before it's too late, in the face of a zombie apocalypse. Somewhat horny.
• Booty Royale: Never Go Down Without a Fight is incredibly horny, problematic trash that's way better than it has any right to be and it actually manages to handle its subject matter somewhat appropriately. Still goes to very gross places and is fundamentally a story about exploitation, but it's also aware that what's happening is bad, actually and has its moral compass characters around to sort of offset that. Several times it stops the story dead to drily talk about actual, real world issues including railing against the Japanese government for its refugee policies being inhumane and racist and the abhorrent conditions in the refugee camps/detainment centers. I cannot in good conscience recommend it in general because of how gross and problematic it is, but it does deserve an honorable mention for how it actually has redeemable qualities and somehow handles its absurdly trashy subject material somewhat appropriately.

Seconding the recs I've seen for Look Back and Goodbye Eri. CSM is good but it is shonen so eh.

I will always take the opportunity to recommend How Do We Relationship?. It's got some of the most realistic depiction of relationships I've seen in japanese media. Keep reading after the heartbreaks; that's when it gets really good.

Idk why it's labelled shonen; people I know who've enjoyed it the most are women. Ig shonen's become a more abstract label these days.

Getter Robo or maybe Tezuka's Phoenix

They don't make manga that's not about high school :3

I have a soft spot for the original Hellsing manga by kohta hirano

Would you like Manhwa? I like Ragnarok Into The Abyss. It's so edgy it's great and it has all the 90's to early 2000's anime tropes.

I guess I like seinen, but I've also enjoyed josei like She Loves to Cook, and She Loves to Eat.

CW: SA

Edit: I take back my suggestion, see below.

Gambling Apocalypse Kaiji. (the anime is excellent, but adapts only the first two parts)

Helck. (the Manga is better)

SoreMachi: and yet the town moves. (the Manga is better)

A few of these are from shonen magazines, and a few have high school age characters in them, but I don't think they break your requirements in spirit.

Boku no Mura no Hanashi — As far as I can tell, there's only one volume available in English, and it's only available online. It's a fictionalized retelling of the Sanrizuka Struggle which is an important chapter in the history of the modern Japanese Left.

Yokohama Kaidashi Kikou — This is a chef d'oeuvre of gynoid fiction and the most relaxing depiction of the middle of mankind's extinction I know of. I strongly recommend it. It's about a robot girl called Alpha who runs a quiet countryside café near a Yokohama which has been submerged underwater. Alpha takes photos, she has human friends and a robot friend, she plays music on her moon guitar and awaits her owner's return.

Non Non Biyori — This is about the lives of four kids in a small farming community in the middle of nowhere: a first-grader, a new kid, and two sisters; and there's also a fifth kid but he never talks. Sometimes the chapters focus instead on the grown-ups around these kids. The anime adaptation of Non Non Biyori is great as well and if you've seen it you won't mind re-experiencing it in manga form.

Akane-banashi — The main character Akane's dad failed a rakugo test and basically gave up on his dreams of becoming a rakugoka after that, and so Akane is sort of trying to avenge him by becoming a rakugoka herself, and she dedicates her all to it and kicks ass. It's top tier.

A Bride's Story — It takes place in 19th century Central Asia. I just think that's cool.

My Journey to Her — Autobiographical manga by a Japanese trans woman. I guess it's been translated into English since I last read it myself, judging from the fact that it suddenly has an English title on Anilist, when it used to be called "Boku ga Watashi ni Naru Tame ni". A positive note is that since this manga was first published, some of the information in it has become dated due to progress in trans rights in Japan.

Yotsuba&! — This one is an absolute classic. The main character is a five year old girl adopted from a non-specific foreign country by a single dad, and the manga is basically just this kid's random adventures. It's the number one most recommended manga for learning Japanese. I guess you can say that Yotsuba&! is kind of like urban Non Non Biyori in a sense.

Aria — This one pairs famously well with Yokohama Kaidashi Kikou because it's in a similar vein of relaxing manga depicting a future which, for all its new technology, is still pretty "rustic". Aria is about a terraformed and renamed Mars far off into the future, where a 1:1 replica of Venice has been built, and the main characters are all gondolier tour guides. It's really imaginative and optimistic. Note however that Aria was originally called Aqua.

You might like The Girl From the Other Side: Siúil, a Rún. I quite liked it and I especially loved the art style.

Also I’m always raving about the Princess Jellyfish anime but the manga is even better and has a lot more content.

Land of the lustrous. It has an anime and the manga is finished.

"Gon" by Masashi Tanaka. No words, just a story using images. You don't have to read them in any order. It's about a dinosaur who survived to the modern day and just vibes around other wildlife. One of the best drawn comics of all time.

I've been wanting an English translation of Shigurui: Death Frenzy, but no official one exists. If you can read Japanese or don't mind fan translations, you'll like it if you liked Berserk and Vagabond. It's about two rival samurai (one blind and the other with only one arm), how they became rivals, how they got their injuries, and how they finally have a chance to kill one another when a mad lord holds a tournament where people fight to the death.

It completely strips away the romantic version of samurai, while showing how awful the caste system in Japan was.