I’m not refusing to see anything, but since you keep mentioning Wi-Fi I concluded that you don’t understand how MMS works.
I upgraded, and my wife upgraded, and neither of us have a problem sending MMS. And I suspect that most of the 500 million iPhones that are eligible also upgraded, and most of them didn’t have problems, because if even a tiny fraction of them did this thread would be 1,000 pages, not 10 pages. So it’s a problem with your phone, not with the specific update.
Did you see the post from Baleca just above? And their post on the previous page about how they fixed it? And my reply to that describing what the Apple genius did to fix it?
Oh, and have you tried Settings/General/Reset - Reset All Settings?