I argue that it's less about having a full idea out in the open and more about being completely honest with your intent.
Something along the lines of
"Hi there, I'm so-and-so. I have an upcoming idea for a fantasy-romance comic featuring dragons, princesses, and knights. I don't have a full plot fleshed out, but I do have some character sheets and written ideas here:
(shows example)
I've done work in mostly fantasy-romance, which can be found here: (show examples).
As of now, I'm just looking for someone to bounce off ideas with (fellow creator, anyone who likes fantasy-romance, etc). I don't really know if this will be a long-term collab or a short-term, but as of now, because the idea isn't fully developed, I would just like someone who is interested to talk about some concepts. Once we have a full idea, the idea of unpaid or paid will become a question."
I honestly feel a lot of these collabs go south because they leave people hanging. They expect everyone to be mind readers or to do to the dms, eager to hear more. But it's just easier to show what you have so far, what you've made so far, and be honest about your intentions, along with being reasonable.
Again, these aren't necessarily set in stone rules. It's less about filling out a form and more about people being able to look at your pitch and go "ok, I understand what you're selling" without needing to ask. Because, as you said before, most people just ignore it if they don't understand right from the start.