Alright, this is an extremely subjective type of question, but here are some of mine with a couple thoughts:

• Sweat and Soap - This is probably the most spot-on recommendation I can provide based on what you said you are looking for. A romance between working adults that are able to do things like communicate with each other to overcome problems together instead of drawn out, contrived misunderstandings. It's great. Also, I haven't read it, but the author also wrote Telework Yotabanashi, which I have seen others say fits this profile as well.
• Love's in Sight! - Reading the synopsis, you might question my recommending this because the characters don't seem too realistic. However, despite heavily featuring a cast of characters with visual impairments, I was impressed with the realism with which they are depicted. I have professional experience talking with people suffering from visual impairments and the issues that the manga depicts lines up with the real-life issues that these people experience extremely well.
• The Girl I Like Forgot Her Glasses - The most unrealistic part of this series is that somebody with such bad vision would forget their glasses as much as Mie does. However, if you suspend your disbelief for that one narrative conceit, then this one feels pretty genuine for a middle school romance. I started reading this series rolling my eyes at Mie forgetting her glasses all the time, but that gimmick lessens over time and the story becomes more heartfelt and touching as it goes.
• Journey Home After School - This is the only ongoing series in my list and probably pushing your realism boundaries the most. However, if you can overlook some fun randomness from Chokki-chan, then this has so far been an excellent romance.

The manga I've read with the most real characters by far was Skip and Loafer. It's great! It's one of my favorites! But honestly I'd say it's only 1/3 romance with the other 2/3 being slice of life and coming of age. Still, I highly recommend it.

If you want something where romance is a bit more of a focus I also recommend Wotakoi: Love is Hard for Otaku. It's a story about a couple of awkward office workers who slowly develop their relationship.

My favorite romance manga though is Kaguya-sama: Love is War. These people definitely feel more like cartoon characters than people sometimes. Not in a bad way (I love how these characters are written), but their traits are pretty extreme for good and for ill. The first few chapters all follow the same basic formula, which might trick you into thinking that this manga is a one-trick pony, but it changes things up often enough that it ended up being one of the most satisfying manga I've ever read.

All 3 of these have excellent anime adaptations by the way, though none of them are completed yet.

• Wotakoi
• Blooming Love
• Obokoi Majo wa Majiwaritai!
• She Loves To Cook, She Loves To Eat
• Sweat and Soap
• Kasane and Subaru
• Telework Yotabanashi

The 1st is a romcom about 2 office couples who are also otaku. The chemistry between the characters is amazing.

The 2nd is a nice and comfy read.

The 3rd follows a middle school couple where one is a witch. The initial premise sounds dodgy, but it's actually not.

The 4th follows 2 women who live close to each other. The title is pretty succint tbh.

The rest are by Yamada Kintetsu. Also adult romances. They're absolutely brilliant at writing sensible characters and rarely use the stereotypical tropes.

Here are a few lesser known manga

• Kyou mo Veranda de (is similar to telework)
• Misumi-san Can't See Through
• Tonari no Seki no Yatsu ga Souiu Me de Mitekuru
• Kesa Mo Yuraretemasu (one of my favorite, it is heavier on the comedy and lighter on the romance)
• Alice-san Chi no Iroribata (age-gap romance)
• Ao no Hana, Utsuwa no Mori
• Haru no Noroi (a very dark romance, with some elements of suicide)

I don't really read any romance, but I really liked My Monster Secret: Actually I Am.... More of a Rom-Com. There's also an anime adaption that's sub-only.

Edit:

Meet Kuromine Asahi, "the man who can't lie". On his way home, he just learned an important secret: his crush, Shiragami Youko, is actually a vampire! Can Asahi actually keep her secret?

It's a fun, clumsy, one of a kind vampire romantic comedy!

A few of the titles had a limited print run and can be very hard to find under $150, but ebook versions should be normal price. I still need volume 7 but it's like $200 💀.

Edit 2: just reread post.

I would prefer one where the characters feel real, no the imaginary or stereotypical prefect "woman or man".

Each character has a few glaring faults that make them feel more real. None of them are "perfect" in any way.

I was thinking of how I found some of the ones I've really enjoyed recently. Mangadex has a decent filter system that can have inclusion and exclusion criteria, like must have ninjas but can't have lolis. And the most important criteria of all: only showing ones that are completed. Some of us aren't made to read things as they trickle out only to have them suddenly cancelled (looking at you, Dress up Darling).

I just use it to describe what I'm looking for and then sort the results by rating. That's how I came across Alice-san Chi no Iroribata (others have mentioned it) and Ao no hana.

For ones not mentioned elsewhere:

Sono Koi wa Ichigo no Youni - Strawberries and farming and romance.

Insomniacs after school - I usually can't stand a school setting, but really enjoyed this. Astronomy themed.

characters feel real, not the imaginary or stereotypical prefect "woman or man"

If I'm interpreting this criterion right, it means you don't want a character like Usui from Kaichou wa Maid-sama!. I can't think of a good way to describe these characters. I realised this is just a rephrase, but: they are so flawless, and no such person can exist in real life.

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I think these may fit your definition of "real":

• My Boyish Girlfriend Is Too Cute - A cute couple and you can guess what the girlfriend is like based on the title. The boyfriend is based too.
• Gal Can't Be Kind to Otaku!? - Looks like a rare throuple romance.
• Love Bullet - The story follows a group of modern-day cupids. They haven't been the focus of romance in the manga so far, but let the author cook.
• Managing a Wild Idol - This one is about an idol with serious gap moe and her manager. I think this one may fit the criterion of "real" best.
• I Decided to Fake a Marriage with My Junior to Shut My Parents Up - A very short yuri story at just 3 chapters long.
• Kaguya-sama: Love Is War - You have probably read this, but if not, now is good time to pick this up.
• A Story About a Very Ordinary Couple - A slice-of-life series that follows a very adorable couple doing couple-y things. You may want to read the prequel - A Story About a Man and a Woman and When They Sleep Together, Money Appears Out of Nowhere - first.
• Please Bully Me, Miss Villainess! - A yuri villainess isekai manga. This one is my favourite out of this subgenre.
• Kubo Won't Let Me Be Invisible - The male protagonist is so unnoticeable that it's basically a superpower. He gets hard-countered by the female protagonist though.
• Kuno Chiyo The Psychic - The female protag tries her best not to be rizzed by the male protag because of what the future brings if she did.

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Unsure if they fit your criteria - because it's been a while since I read them- but they are good:

• Beauty and the Beast Girl - A twist on Beauty and the Beast by having the Beauty be blind and the Beast be a lady.
• Sheep Princess in Wolf's Clothing - A yuri romance between a princess and her female butler.

I'm recommending just the 10/10s that I've read, otherwise the list would be too long.

P.S. I noticed there's a serious lag of yaoi in this list. Too bad.

the full time wife escapist if you want something that’s more about realistic characters while also challenging the patriarchal dominance that so many Japanese romcoms fall into though (mild spoiler, I don’t know how to use the spoiler tag) the ending is a bit unsatisfying on that front. It cheapens it a bit but not enough to ruin what is ultimately a great and often overlooked series

Also the translation of the title is garbage. The translation of the manga is good but I have no idea why they settled on such a shit title. They also made it a tv drama and translated the title of that to “we married as job”, which fits better, but still isn’t great. The literal translation of the title is “running away is shameful, but useful” which I think ultimately reflects the work best.

It’s great to read if you’ve felt aimless and disillusioned in your early adulthood (like late twentys/early thirties) as well

I wonder if you would like strawberry panic?

https://anilist.co/manga/33039/Strawberry-Panic/

https://anilist.co/manga/58226/Bonnouji/ is mostly normal adults.

https://anilist.co/manga/110140/Futari-Ashita-mo-Sorenari-ni/ is exceedingly normal adults.

https://anilist.co/manga/106983/Arasa-Dakedo-Hatsukoi-desu/ is stereotypical naive adults.