I may be missing the essence of OP’s question and definitely do not intend to hurt/offend anyone, but my (40F who also wears about a 40F bra) perspective is that breasts are generally sexualized amongst human populations (I’m in Canada, but I’ve travelled internationally a lot and know this isn’t just a Canadian issue). If a breast-haver (typically a woman) chooses to display parts of her breasts publicly, I think she shouldn’t be surprised if she receives sexual-type attention directed at her cleavage. Personally, I wore some revealing clothes in my younger days and have subsequently (within the last 10 years or so) made the choice to cover my cleavage in public by wearing clothes that come up close to my neck, but we’re all free to choose how we represent ourselves.

I think of it as a matter of “there’s a time and place for everything,” meaning there are times where it may be suitable to play up one’s cleavage (e.g., in social setting like nightclubs where the norm is to dress so as to attract attention) and times (like working in a conservative office, when the attention would ideally be on one’s mind/abilities rather than breasts) to tone it down by choosing to display no cleavage. For me (the way I dress myself, I mean), the clothes I have that could show my cleavage simply aren’t acceptable (to me, for myself) to wear in an office environment. Some women are comfortable displaying cleavage everywhere, all the time - I’m not judging them for that, just saying that a whole lot of people feel differently and are uncomfortable with seeing boobs on display in the office.

As an aside, I’m aware of the argument that women/girls/everyone should be allowed to wear whatever they want and that society should instruct others (primarily men) not to sexualize women/others in general when revealing clothing choices display a lot of skin/sexualized body parts. I believe that this should be true, but it isn’t actually true today. While a cultural/societal mindset shift like that could be achieved over several years or perhaps generations, I don’t think it’s necessarily going to happen any time soon. Thus, we currently have the breast-sexualizing culture/society we have, and we can make personal clothing choices accordingly (in line with how much attention we are each willing to accept or choose to decline, based on societal/organizational standards and our own dressing preferences). All things considered, in my culture/society, I don’t think anyone (straight size or plus size) should be surprised that showing cleavage attracts more attention than wearing less-revealing clothing does.

TL; DR: I guess my personal bottom line is “show them if you want the attention, cover them up if you don’t.”