Doujinshi (同人誌), also romanized as dōjinshi, is the Japanese term for self-published print works, such as magazines, manga, and novels. Part of a wider category of doujin (self-published) works, doujinshi are often derivative of existing works and created by amateurs, though some professional artists participate in order to publish material outside the regular industry. - Wikipedia
Doujin are mangas but created/drawn by fans. So I guess you can say whitelabel manga, but they use popular IPs and sell them to showcase their skills.
ahh I thought doujin manga are the boy love ones or something 🤣
Lol no, doujinhi means