I don't want yaoi ....I don't want yuri
a shoujo manga where the guy crossdress / transform into girl (maybe magic) and fall in love with the girl(mc)

so technically it's still boyxgirl...

for example:
- Kuragehime
- Dare nimo Naisho
- Kanchigai Hime to Usotsuki Shimobe

thank you...
(hope you can help me)

There's:
W Juliet
Usotsuki Lily
Mizutama Honey Boy

You may find more by doing a Genre search:

https://www.mangaupdates.com/series.html?page=1&order by=rating&perpage=50&category=Androgynous%2Bm ale%2Blead_Cross-dressing&filter=some_releases&e xclude_genre=Ecchi_Shoujo%2BAi_Shounen%2BAi_Tragedy_Y aoi_Yuri.

I've included the tags "cross-dressing" and "androgynous male lead". Have fun!

thank you, I try reading them

idol pretender

Kanojo ni Naru Hi - It's about a guy who falls for his guy friend who becomes a fully genetic girl. I know it's know what you are asking for, but it's one of the best gender benders I have ever read.

Charming Junkie! Manga about models with some beautiful morals, but even more beautiful art ❤️

AKB49 Renai Kinshi Jourei- a guy crossdresses to join an idol group in order to secretly support his crush.

Otonari Complex is about two childhood friends, where the guy crossdresses (at times) and the girl gets mistaken for crossdressing because of her boyish appearance, athough the story is set in college rather than your typical highschool setting.

Magical Change (a high-school boy is given a magical power, when he uses it he turns into a girl)
Yukarism (when the main guy falls asleep he wakes up as woman)