I love a novella. I didn’t look up page counts but here’s some I remember being shorter and worth reading

• Bartleby the Scrivener by Herman Melville
• Ethan Frome by Edith Wharton
• Notes from Underground by Fyodor Dosktoevsky
• The Death of Ivan Illych by Lev Tolstoy
• The House on Mango Street by Sandra Cisneros
• The Island of Doctor Moreau by H.G. Wells
• The Overcoat by Nikolai Gogol
• The Nose by Nikolai Gogol
• The Pearl by John Steinbeck

https://libraryofshortstories.com/

By the Waters of Babylon may be my favorite short story I've read.

I assume other genres probably have them, but for scifi there’s a lot anthologies that cover short stories. I like them that the stories can be read in a session, sometimes multiple. One of the shortest I’ve seen is Isaac Asimovs postcard story, fits ona postcard!

Scifi that was the only way to get published way back when, scifi was seen as too risky for long form printing.

In scifi, it’s even goes further into themes so you can pick what you like. Examples would be ghost stories, or time travel, detectives, space ships only. Stuff like that.

Some free options.

Sorted by "Shorts' then length.

https://standardebooks.org/subjects/shorts?sort=length

Harlan Ellison has good scifi horror ones. I have no mouth and I must scream and other good ones

Turn of the Screw - Henry James

Clarksworld

Monthly SciFi short story publication. Each month they release about 6-8 short stories. Its free on the website, but if you want the epub or physical copy, it costs a few bucks.

https://clarkesworldmagazine.com/

Clarkesworld is a monthly science fiction and fantasy magazine first published in October 2006. Each issue contains interviews, thought-provoking articles, and between six and eight works of original fiction. Our fiction is also available in ebook editions/subscriptions, audio podcasts, print issues, and in our annual print/ebook anthologies. Clarkesworld has been recognized with a World Fantasy Award, three Hugo Awards, and a British Fantasy Award. Our fiction has been nominated for or won the Hugo, Nebula, World Fantasy, BSFA, Sturgeon, Locus, Shirley Jackson, Ditmar, Aurora, Aurealis, WSFA Small Press, and Stoker Awards.

The cover art is also very good imo

The Quiet Boy, it's free online, unfortunately can't remember the author. Lovely and spooky

If you like weird then check out Richard Braugtigan

Ray Bradbury is my absolute favourite short story writer.

Plays are also good options. I loved the Crucible by Arthur Miller when I read it earlier this year.

I love this by Hillary Mantel. Her book of short stories (The Assassination of Margaret Thatcher) I also thought was good.

"The Yellow Wallpaper" is like 25 pages and pretty good I've heard. Its on my Xmas list.

Welcome to the Monkey House by Kurt Vonnegut. Its 25 short stories on 352 pages though, so on average 14 pages.

Cuentos de amor de locura y de muerte

Ted chiang (either exhalation stories or, stories of you life and others). It is shameful no one has mentioned him yet.

Kelly links short stories are good, if a bit weird. "Magic for beginners", and "get in trouble" are two collections.

Nebula anthologies are sometimes excellent usually have some short stories and a novella.