If you're looking for manga similar to B-PROJECT 3rd Season, you might like these titles.
Mana Nagase is a high school girl from Hoshimi City who loves to sing. One live performance leads her to become a top idol and she starts to shine.
To-Y (Fujii To-ii) is a member of the punk rock band GASP. Along with other punk bands, which usually just hanged out doing small gigs, they have this enormous hatred and aversion to the main Japanese music industry, which is dominated by pop music and untalented Idol singers. However, To-Y was tempted by Kado (the Nagel ripoff) of Kama Production, a strong will promoter, to expand out beyond GASP since he has the talent, except she also expect to promote him as an Idol singer, which revolts To-Y.
Azuki, a young girl whose father is the president of an entertainment corporation, is always out of luck when it comes to dating. It seems like every boy she had dated before all tried to use her as a bridge to get into the world of media. So when Azuki met the guy of her dreams, who also happened to be a contestant in the audition her father set up, she wasn't so sure what to do anymore.