tried the suggestion forum before, but here i go again:

Can someone suggest me some dramas that center around FRIENDSHIP, like the formation of a Friendgroup, preferably in high school but not necessary?

Nobuta wo Produce. Exactly what you asked for, HS friend group formation. I loved it. Actually, I loved it so much that I also want suggestions of similar dramas, but I don't have any to add.

Brush Up Life is the best I've seen for female friendships. It's complicated and I found it hard to get into, but once it hit its stride it just got better and better.

Summer Strike

(has a bit of romance but mostly friendship)

Shujin-ko 2019

Kashimashi meshi 2023

Ichiban Sukina Hana (slight romance)

Kimi no Hana ni Naru 2022

Its summer film 2021

Muchuu-sa Kimi ni 2021

Maiko-san Chi no Makanai-san 2023