7-Zip is free software with open source.
Since "BBMJ8.7z" is not a widely known public dataset or standard challenge file in my current database, could you clarify:
(e.g., a specific competition like HTB, TryHackMe, or a university course).
You need to know the metadata or origin of the file.
You need a step-by-step walkthrough of how to find the hidden flag inside the archive.