Flatline's Twitter, Tumblr, and Pinterest presence isn't showing to any major degree.
Type
"Yara" in Twitter and it'll autocomplete to "Yara Flor" and even Yara alone has heat. Do the same with
"Flatline" and the top listing is Immortal Hulk: Flatline via a tweet from Declan Shalvey. Then Apex Legends' Flatline and then a ways down a Joshua Williamson tweet about that Flatline.
Tumblr Yara Flor:
https://www.tumblr.com/search/dc+yara
Tumblr Flatline:
https://www.tumblr.com/search/dc+flatline
Hell, Ghost Maker's search result is longer:
Tumblr. Pure effervescent enrichment. Old internet energy. Home of the Reblogs. All the art you never knew you needed. All the fandoms you could wish for. Enough memes to knock out a moderately-sized mammal. Add to it or simply scroll through and soak it up.
www.tumblr.com
I'm not saying there's none, I'm saying the character not currently a breakout elsewhere.
I was mentally taking Miles and Kamala as a slightly earlier generation, but I guess that does sync up with like Aqualad.