Same issue. Same missing manual detection button in display settings. This is my first MacBook and given the laundry list of bugs I've encountered in MacOS, will probably be my last. I've tried every proposed solution I could find online. Also called AppleCare, and they couldn't figure it out. Their only guess was that my monitor was incompatible, but they don't have a compatibility list. So, even if I buy a new monitor, no way of knowing if it will work. I'm speechless.