I'm feeling kind of nostalgic. I'm looking for any manga with a story that's set in the 1980s or the 1990s (or late Showa/early Heisei), but wasn't actually released during that time. So it would have to be a work that was released in the 2000s, 2010s, or even this year.

I understand that actual 80s/90s releases would reflect the era more accurately, but I think it's fun to read recent works that try to approximate that time period with a more modern art style.

Something other than the Higurashi series, please.
I already hopped on the Erased hype train a few years ago, and that was a wild ride.

If I've made a thread in the "I'm Looking For..." forum, I am only interested in Japanese manga. I am not interested in non-Japanese media at this time.

High Score Girl is the first thing that comes to mind.

Parasyte Reversi due to being a side story to the original. The easiest marks are biographies like Steve Jobs or manga about the history of the industry as Aoi Honoo.

I also read EU/US comics and am a librarian.
Manga-Masters, My ANN-Lists + Imdb

it doesn't take place in the 80s but if you're into the 80's vibes try Slow Motion wo Mou Ichido

There's a tag for Showa Era if you're interested.

As for actual series, the first thing that popped to mind was the Shimizu Aki adaptations of Kyougoku Natsuhiko's novels, ala Ubume no Natsu, Mouryou no Hako, etc. Though not sure how closely these fit into your request, since the manga adaptations are modern, but the original works were actually written in the '90s.

Other recs...
Asadora!
Usotoki Rhetoric
Yuureitou