First off, I think I'd like to address the larger point of Lemmy's toxicity.
I think Lemmy is quite unique in that while it is fairly progressive leaning, it also may be a rather poorly socialized overall. The whole selfhost/Linux community which is at the heart of Lemmy's identity doesn't exactly have a great track record of being super thoughtful in our communications.
There's a persistent need to "be right" that is common here, because being intelligent and independent thinkers is part of our identity. But that can often manifest in toxic ways, and disrespectful communication. Many of us are trying our best to not give in to this toxicity, but it still does manifest regularly.
I think men's lib spaces tend to be a bit more respectful because they acknowledge that the patriarchy affects them negatively as well, and this diminishes the hold of toxic competitiveness.
Anyways, enough about that, and on to your question.
IMO, the best way to be a good ally is to just participate earnestly. Part of being a man who acknowledges the damages of the patriarchy also makes it hard for them to be vocal participants in women's spaces. That means that we often aren't party to women's perspectives, or don't feel comfortable requesting more information, even though we genuinely appreciate your experiences and advice.
Women as a group seem to me to have a much stronger sense of camaraderie than men. The feminist movement is also much more developed as a resistance to patriarchal forces, whereas men's lib doesn't have nearly the same depth of development, as it's a younger and less cohesive movement.
That's why, just being present and willing to share your experiences and thoughts in an open manner is so beneficial.