Connecting to the remote endpoint just spews a bunch of text in a constant stream. Based on challenge description, flag must be in there at some point, but would be impossible to catch with your eyes.
Redirect nc output to a file for a few seconds, and then grep for flag. If matches, open and ctrl+f for `flag{`, else, extend nc+grep time.
[Full writeup](https://bigpick.github.io/TodayILearned/articles/2020-06/nahamConCTF-writeups#vortex)