Penis enlargement and breast implants can be understood as gender affirming surgery for cis people, it is just an affirmation of the gender assigned at birth. Rather than go to primates I would point to ancient Greece and it's statues to make the point that ideals of gender and bodies shift over time. Greek statues shows as I understand it often an ideal body, which by the norms of its time included a rather small penis. So maybe some male ancient Greeks wished there were treatments to shrink their package?

With gorillas, my understanding is that primates that have very unequal sizes between the sexes has small penises, while its among the primates with roughly equal body size you find larger penises. So akin to plummage, the males showing off of that their bodies can afford to waste resources, and thus presumably is very fit. I am no biologist, but I think this means that if you try to win a domination fight with a gorilla, it may show who is the boss by showing off its physical strength. So not recommended.