Thanks for your answer. I wouldn't define being open in the workplace as "don't hide it on facebook, instagram or other social media". I know borders can be blurry between what's private and what's professional, but to me being open in private circles is definitely not the same as being open with your colleagues. I know it's far from perfect, but that's the best definition of "open" I can offer yet.
I am myself gay, so I may be biased on the sample of other LGBT economists I know, but at least in my department (that has a reputation of being usually nice and welcoming), I have never, ever heard any of the LGBT researchers or faculty openly discuss about their daily life stuff in various social events. In some occasions, it even took me *years* to know if someone was gay (even though I had my suspicions, but asking directly to someone "are you gay?" is one of the worst possible aggression you can do to a LGBT person). I am myself not open, and I have zero plan to change that. In other departments, I know people who are usually vocal about their politics being incredibly discreet about their sexual orientation – which is fine, I don't judge, I just try to understand why. Overall, I am not sure I know any truly open LGBT economists except two, or three (all women, for that matter).
Also, I wouldn't use some (disputed) numbers on the general population to infer the proportion of LGBT researchers. Mostly because as shown by the first link in my question, the distribution of people on jobs according to their sexual orientation is not job independent (so there is no reasons to assume researchers are similar to the average population). And also because measuring sexual orientation is hard (people can lie, people can even ignore they're gay, for many people sexuality is fluid, etc.), even though if I recall correctly, the number considered as the good one among psychologists is more of 5 to 10% of the general population who is gay of some sort.
I personally believe that economics is, in general, a field historically and currently made of, and by, white straight males, which shapes the structure of power and the associated incentives for anyone who wants an academic job. I'm absolutely not saying economics academia is homophobic, nor that being a white straight male is a bad thing. I'm rather saying that due to the way economics (as an institution) evolved and evolves, it's probably some sort of second best for a LGBT person to "hide" it somehow (people respond to incentives. And I don't think incentives in academia take really well into account the issues faced by some "minority" groups, like women, PoC or LGBT). But I could be wrong.