This query appears to be highly specific and potentially refers to a challenge, a specific malware sample, or a unique file identifier.

did you encounter this ID (e.g., a specific competition, a website, or a file name)?

What is the of the FLV file (e.g., are you trying to recover data from it, or solve a puzzle hidden inside)?

To provide the "helpful write-up" you are looking for, could you please clarify:

: It might refer to a specific commit or file ID in a private codebase or a very recent upload that hasn't been fully indexed by search engines.

The string 21juakq87klo61 does not match widely indexed public documentation, which suggests it could mean a few different things:

: In cybersecurity research, long alphanumeric strings often serve as unique IDs for files (like MD5/SHA hashes) analyzed in sandboxes.

: It may be a specific hash or identifier for a forensics or "misc" challenge involving an FLV (Flash Video) file, often found on platforms like Hack The Box or TryHackMe.