Simple data breach is mean someone breaching the victim data so let's called (Database) this can be done in many way like (Malware, Worm, SQL vulnerability, XSS vulnerability,IP hijacking,DNS hijacking,WAS vulnerability, etc) as you see you done it in many way depending on your skills.
well also we have others data leak like (Video,Image,CSV,Invoice Report,etc) like 16 years old kids spread the Spyware to someone on Rockstar company they lead to leak & get the private project working on it Rockstar company do it its (GTA VI) also the Indian guy install backdoor on some sony entertainment supervisor system the lead a 10 years futures sony project to be leaked & sold them back for 2.5$ million via Monero crypto for her safety,Also shadow broker group it's some arab hacker lead Microsoft company leak which is worth 1B$ then they sold to some Chinese guy for 5M$ on deepweb. Also many intelligence agencies of the largest countries lead to be leaking yearly.
Final word data breach is most hardest part on cyber security it's require a high & expert skills in many injection techniques mostly (Database injection)
as admin mentioned in the forum there's too many leak you can find