I'm looking for romance mangas that are uncommon. Not the typical knight in shining armor and damsel in distress, prince and maid, and etc...

Takane to hana, a bit cliche at times but the girl is far from being a damsel in distress

Perhaps a bit old, but Kare Kano is one of my favorites that would come under that.

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Kaguya-sama wa Kokurasetai

Beauty Pop

Oboreru Knife
Mahou Tsukai no Yome
And if you're up for GL - Tamen De Gushi

That depends on what you mean by uncommon.
But I've read a lot of manga

After thinking about it and getting some help I have one recommendation.
From maid to mother, relativly new currently under 20 chapters if I remember correctly

M-chan

I second Takane to Hana and Mahou Tsukai no Yome. Also Kare Kano is a classic.

I recently fell in love with Koushaku Reijou no Tashinami which is definitely an interesting take on isekai stuff. There is a prince though, two actually, but you can say the maid is the rival.

There's also Beastars which is definitely uncommon in a lot of ways and the main character is male. It's also definitely not shoujo.

Otoyomegatari is also always a great rec for romance and strong female leads with no knight in shining armor. Also the art is just gorgeous always.

There's probably a bunch more that I can't think of right now so I may be back, though is there anything else specific you're looking for aside from uncommon romance?

Must Read Webcomic:
Unsounded

Lists:
Reading
Complete
Western Webcomics

Cubism Love - Girl's brain/soul is in a box and has no body.
Diamond Life - Woman who unwittingly fall for a man

HIV positive and how she comes to term with it.
Don't Cry, Girl - comedy about girl falling for a man who 's a nudist.
Hot-Blooded Woman - Girl soul is temporary in another's body and the guy she falls for treats that person like trash, but she wont stand for it being looked down upon.

Some I highly recommend:
flowers of evil - if you don't mind incest or Manhwa.
oboreru knife - someone already recommended this but I reposted because it's a beautiful manga with an unique set of of characters and execelent development.

mars - pretty old manga that is well known yet I found many have not read it yet.
six half - (also incest)
true love - incest, cute art similar to sakurada hina's style.

The sleepy residents of birdcage manor - interesting story with atypical characters
eden no hana- incest warning.
nocturne- love interest is older and the adopted father. Manhwa.

the one - so long but so good.
Issho ni neyou yo - love between a runaway girl and guy who won't take mask off his face because of mommy issues.

hana no namae- huge age gap but it's whatever.