梗 is borrowed from the
哏 (gén) of crosstalk (
相声) culture — a 'punchline' or 'comedic hook'. On the internet
梗 means a meme / running joke / inside reference.
玩梗 is 'to play with the meme' — riffing on, layering, or referencing it. The verb cluster:
造梗 (create a meme),
玩梗 (riff on it),
烂梗 (worn-out meme),
梗图 (meme image).