What is the ruling on my participation in mixed-gender forums, knowing that I interact respectfully with men and within the scope of the topic, while I interact with women with jest, laughter, and fun, and men may see that?

It is better to stay away from mixed forums. Women-only forums are sufficient, and this is safer for your religious commitment. One cannot guarantee that a man will not comment on your posts, which could open the door to exchanging pleasantries.