Anime that are good; I have no idea if it fits your needs, though. Funnily enough, I don't actually watch that many Romance and Slice of Life stories to begin with.
First of all: I would like to add some qualifiers for what I'm about to recommend.
Qualifier 1: It's hard to find any romance with not at least one or some other people attracted to the MC, no matter if it's male or female lead. It also has something to do with showing the LI that there's competition. But there's still a huge difference in how "big" this crowd of "others" is and how present. And even if they are present, how obvious is it that they would take the main girl or guy?
I will therefore include those with a harem that isn't all that pressing.
Negative example: Ouran High School Host Club. I always thought it was pretty clear which one she chooses, but at the same time, they try to make it seem as if the other guys had a viable chance. Another good example would be Akatsuki no Yona. While, yes, it seems kind of obvious who's going to be her male lead, but at the same time, ironically, it's the guy who killed her father that's portrayed as a "technically still alternative love interest".
Qualifier 2: You mention a lot of Genres and they are all seperated from each other. Romance even doubles, with Romance and Romantic Comedy. Therefore, I take the liberty to assume it doesn't have to be all of the above and it could just be "Slice of Life" without Romance in it (realistically, there will be a bit of romance in almost anything, even the most basic Action flick, but it won't be front and center).
Shows
Violet Evergarden
There is a romance that drives a lot of the protagonists actions - in fact, it her sole motivater in why she does the things she does - yet it isn't present, as the love interest isn't present. It's Slice of Life with a few bits of Action now and then. Mostly Drama though.
Ghost Hunt
This one is a bit outside of what you were asking for; the romance isn't really present and it's not Adventure, but mystery. But it's an often overlooked, very good watch and Naru-Chan is a mood.
Why Raeliana Ended Up at the Duke's Mansion
It's sadly one of them slop anime produced cheaply at the behest of CruchyTroll, but the story is actually great. I got the Webtoon collected right behind me; it's one of the VERY few hetero romance stories that I loved to read, because the main couple slaps. It's funny, the protagonist has people who are interested in her, but it's not actually a harem and the male lead is clear from beginning to end.
The Saint's Magic Power is Omnipotent
It's not that deep and it's not complicated either, but it's entertaining enough. It's a fluffy two season finish. Romance front and center in an Isekai setting.
Snow White with the Red Hair
It's cute, again, there's other people interested in the protagonist with this one, but it's not a "harem" that can be taken seriously.
It always depends. I'm usually annoyed with "reverse harems", which are just harems, but people like to make that difference, when the person in the middle is female. In the end, when a female author writes, you can tell the emphasis on emotion and that fucks, because it's usually way deeper than the superficial sexual attraction of "regular" harems. Meaning, the slighted guys left and right will remain sad in their unrequieted eternal love somewhere around the already married with children female MC forever - or at least that is usually implied.
It's the same for this one, but they aren't as egregious.
Pass the Monster Meat, Milady!
That's a pretty new one and it's funny as fuck. Let's be real. Not harem, as far as I'm aware, but I've mostly watched the first 5 episodes. It's mostly about food, to be honest.
Beck
It's a music Anime - Drama and Slice of Life. Romance is a sidetrack, but it's not harem and it's cute. Also, it's a cool story.
Chrono Crusade
Okay, this one is completely different from what you were asking - it's about demons, it's action and fantasy. But it's great, you should watch it. And yes, it's female lead with a romance as a substory. No harem.
Doctor Elise: The Royal Lady with the Lamp
Not really a harem, but there is, technically, another guy interested in her. But the main conflict is a different one and it's kind of not even a question who the guy is she will end up with. I also don't think the hint of the second male lead is that strong.
Slayers!
Okaay, now I'm really trailing off, but it's adventure, there's a quirky romance in it and it's old but gold.
Movies
Your Name.
This one is Romance and Drama front and center. The protagonist may have his moments, but he's not really pervy, just in case you are wondering, as soon as you get down to watch it. It's a movie from the Japanese Anime equivalent of Nicholas Sparks (in other words Makoto Shinkai).
The Garden of Words
I once bought this for my sister, who isn't much into anime and she liked it.
Weathering With You
Classic Makoto Shinkai Movie.
The Anthem of the Heart
This one is more Drama than romance, if I remember correctly, but it's been a while since I've last seen it. Another one I got for my sister - the things is: again, Romance or even just Drama / Slice of Life is not my forte, if it isn't Gay Romance or really interesting for whatever reason. My sister is more of an audience, so I take her word for it and she liked it. I also remember not disliking it, which is alot coming from me.
The Garden of Sinners
Yet again one which kind falls out of line, but since it is indeed my favorite Anime movie series, I wanted to mention it. There IS, in fact, a Romance in here and it's not inconsequential either, but Action is still more prominent among the Genres of this one. Story slaps, you should give it a watch.
Also, also, in terms of great comedy, I can recommend Sword Art Online Abridged. They turned those two characters into total variants sociopaths, which makes their developing relationship pretty fascinating.
That is actually true. In fact, it's so much better than the original.
I mean, in terms of what SAO is, almost anything is better than the original, but it did have an interesting premise. SAO Abridged (I don't even feel the need to say it, but I will add: By "Something Witty Entertainment" on YouTube) takes this premise and the shit load of absolut brain rot in the original and takes it to new heights.
With all the slap stick humor in it, it makes everything feel so much more relatable and realistic - from avatar names like "BallsDeep69", to Kirito's tirade about how much he hates humanity and yet still cares about it (which is, ironically, so much more impactful; has so much more to say; is so much more considered than the original scene, which is SUPPOSED to be a dramatical highnote), it's just so much better. It's what SAO SHOULD have been - minus the satirical humor, because it was originally meant to be serious. To be honest, as they patched up all the plot holes from the original story, one might say it's less ridiculous, since it can be taken more seriously.
There you go, a literal satire can be taken more seriously than the original story.
