there all a zillion "answers" for this issue; here and elsewhere, type 1: it's right here Settings -> Privacy & Security -> all the way at the bottom. You're welcome. except when it's NOT there. at all. posters don't READ the problem. type 2: here's what worked for me (no mention of HOW MANY TIMES they tried the same thing and it suddenly worked). list of steps that if YOU follow will not work. type 3: here's The Definitive Way to fix it: Unpair all your devices. reset all of them to factory settings. close xcode. turn developer mode OFF on your phone (includes restart). hold your phone between your knees while spinning around in your chair 3 times clockwise, then 3 times counter-clockwise. turn developer mode ON on your phone (including restart). but that's a "real" restart, so do a complete hard restart. turn off your watch. turn on your watch. etc. i got both of my reset phones back to showing developer mode in the right place, but the number of steps / tries / retries / restarts / with or without plugging the phone in via cable. i have no recollection of WHAT WORKED. it would certainly be handy if Someone @ Apple Support would post a KB about How To get Developer Mode to show up as an option in Privacy & Security. for sure. these steps. in this order. these questions go back YEARS with most people stumbling over the "solution" when they FINALY get the Dev mode visible again, they just get ON with what they were trying to do in the first place. or - you know - FIX the problem in the next iOS update.

not sure if it's meaningful, but my latest attempt at least did somethings differently. odd thing was when watch was being paired (on the iPhone app) it popped a message that an UPDATE was required. not so (unless they're counting any "beta' releases). so it spun a bit - but it appears to do Nothing. but maybe it thought it OUGHT? anyway - still broke.