Typically FFS (Facial Feminization Surgery) is done later on in the process but I doubt Jenner is undergoing any such process. Instead I think in typical Hollyweird fashion (i.e., trying to remain relevant in an irrelevant world) he is undergoing FFS2, aka Facial Fookup Surgery (trying to be nice about it here).
Jenner's life is pathetic and his face reflects this.
Do you suppose some folks become addicted to plastic surgery? Do their plastic surgeons convince them that they can keep them young looking? I have nothing against plastic surgery when done in moderation. It can actually improve one's appearance or even sometimes benefit one's health. For example blepharoplasty (eyelid surgery) can improve a person's vision if there upper eyelids are impairing vision as was the case with mine. While the doctor was cutting my eyelids, he reduced the size of the bags under my eyes, which were a gift I'd rather not have from my ancestors and which made me look like I never slept, which was definitely not the case.
Many people who didn't wear braces to correct an overbite, crowded or crooked teeth when they were kids will go to an orthodontist to have this taken care of as adults. Nice evenly spaced teeth actually is a benefit to dental health as well as looking better cosmetically.
There are some procedures though which are purely cosmetic. Having your lips puffed up or butt implants are a couple of things that come to mind. Boob jobs are another. Botox to erase wrinkles seems like it isn't a necessary procedure, plus they just come back after the Botox wears off.
Some men start taking on a more effeminate appearance as they age. This could have something to do with a reduction in their male hormones or just a family trait. It doesn't necessarily mean they are trying to look like women.
Bruce Jenner is suspect because his more feminine look as of late seems to be a direct result of actions he's taken, such as reducing his Adam's apple and growing his hair long. Maybe he wears Spanx because he is fat (there are Spanx for men) or maybe he likes wearing women's underwear, who knows for sure. I've never met any guy who wore a sports bra to support man boobs, that I know of. The Spanx men's undershirts probably compress and hold a floppy and flabby chest in. Maybe that was what he was wearing in that one photo.