What is the best visual novel dating sim or a game similar to that makes you happy.

Dating sims aren't my thing, but to not leave you without an answer, A Small Hike is a similar(ish) game in a way that it's relaxed, cheerful, positive, bright and all-around pleasant, on a little island that is fun to explore. You can run, fly, jump, swim around, so it has enough active gameplay in it to be involving too :)

I really, really fell in love with Hustle Cat. It's a small game, but a heartfelt one, with both male and female love interests. I'm not even into women, but I still played the female LI routes because I just loved all the characters so much. Magic, cats, and cute guys/girls, what more could you ask for?

That's a good question, really. I tend to like the longer and more dramatic plots for dating sims and visual novels, so I'm not sure most of my favourites would qualify as "happy."

That said, The Rose of Segunda is cute, fun and has excellent personality customization for your character, and while I haven't played any of the EA sequel yet, it seems like it's going to expand significantly on every route in a way I'm quite excited for.

And while it's only a dating sim in the loosest sense of the word (meaning: while you can choose to spend more or less time with a character, no matter what all three of you end up together), Heaven Will Be Mine will always be an exceptionally queer standout as a romance story. The writing in it and We Know the Devil is still some of the best I've seen in any video game.

Plumbers Don't Wear Ties

Huniepop seems like the kind of game you are talking about and is free for the next 18 hours.

I'll recommend any VN from one of my favourite developers, PixelFade. Rising Western indie studio with tons of dedication to polished story, branching, characters, voice acting and script, delivering a solid high quality lighthearted romantic comedy every time. They have a couple of subgenres across their current portfolio, all games with 90%+ ratings.
If you're willing to trade the dating mechanism for more of a direct story, I'll recommend my other favourite dev, Studio Élan, specializing in touching sapphic novels - happiness is literally in one of their titles. Expect more of a feelings rollercoaster here.

I don't like much VN, but there is a dating sim that made me happy :
https://store.steampowered.com/app/1019450/Table_Manners_PhysicsBased_Dating_Game/
100% recommend this one (from a bundle hey don't get this full price) !

Clannad. It has some sad moments, but it mostly aims at making you feel happy, ending included