I’ve spent years arguing with people online and really have nothing to show for it aside from my own education and amusement. I was radicalized by discovering r/chapotraphouse back in 2018 I think. Nobody argued with me there, I just lurked, loved the memes, thought it was the funniest place online, then started reading theory because so many people there talked about it. Even though liberals are obviously ignorant about communism, their ignorance is willful: they never thank us for educating them, they always get angry and double-down. (In real life, it’s much easier to embarrass them and get them to shut up.) Still, I admit that it’s possible to change someone’s mind in an online debate, I just haven’t seen it happen when it comes to communism (libs on r/changemyview can change their minds about lib shit). Have you ever seen a lib admit that they were wrong about communism?
The vast majority of forum users are lurkers, not posters, and you're much more likely to change your opinion when you're just reading along instead of entrenching yourself in your existing beliefs (as arguments tend to do).
I do think arguments have some positive effect on some participants, it just takes longer for them to come around.