One of my characters will actually state his sexual preferences, because it's part of the plot. One part of it will be revealed not in a romance setting, but rather in a discussion about social expectations. For other characters, it will remain unknown, or be deducted by who they are interested in (which may mean still partially unresolved, especially when the author is pan like I am!)
I don't really imagine announcing sexual preferences without an actual need for it. I think it would sound weird, not very natural, and maybe even a bit upsetting (but for that last bit, I suppose it would depend on context).
However, if for some reason you want the other characters (and the readers) to know, I think it can be relatively easy to find a way to say it naturally, by triggering a discussion about it in the group; in a modern setting particularily, it can be pretty easy to find an excuse to discuss such things, starting by something that is not personal, but that may push some characters to confide to some others. If it's done tactfully that would not be an issue to me.