Sorta odd that we have this option, but no documentation on it, and no one (except Apple engineers) know what it does. I had seen that post - it was the only link I found to the exact text of the title.

THANK YOU SO MUCH! I did as you suggested - I rebooted my Mac, and d*mn I can now get it to work!!! I'm running the Thumbnail Extension in Xcode, added breakpoints, and NOW they get hit. BTW - it's just not obvious (IMHO) from the docs, but the thumbnail is NOT the view that is shown in Finder windows to the right of the files (when you select a file). That is a Preview view. The Thumbnails are shown in Finder windows (list or icon view) - so they are pretty small. Maybe there are other views you see them in? PS: using latest Xcode and Mac as of 11/2025

Now it's even worse - I deleted the watch from the Xcode Devices window, thought I'd add it again, but I can't get it to show up. iPhone connected via wire, all three devices on the same WiFi network.

I made more progress but the operation is still failing: I unpaired my watch then re-paired it I tried many times to get the watch to show the "Developer Mode" option - it would just not show it. Finally I restarted the phone, restarted the watch, insured both on the same WiFi network as the Mac, plugged the phone back into the Mac with Xcode running, and voila - I was finally able to enable it. Now, the watch showed up in the Xcode Devices window, but I got the same error as I originally was getting. Now I'm suspecting Bonjour, so I restarted my Mac, and rebooted my TP-Link Archer 8 router (has latest firmware). Now, Xcode can connect to my watch!!! It connects and tries to read the symbols, but fails with an alert in a window. Clicking on the window, I was able to copy the error: Failed with HTTP status 400: bad request Domain: DataGatheringNSURLSessionDelegate Code: 1 User Info: { DVTErrorCreationDateKey = "2026-04-07 13:10:58 +0000"; } Failed with HTTP status 400: bad request Domain: DataGatheringNSURLSessionDelegate Code: 1 System Information macOS Version 26.4 (Build 25E246) Xcode 26.4 (24909) (Build 17E192) Timestamp: 2026-04-07T09:10:58-04:00 I keep trying - disconnected the USB cable from Mac to iPhone. Now I get a different error sequence - Xcode connects, fails with a "transport error", and retries. It's now in a loop: PS: every device has the latest software on it: Mac, iPhone, iWatch and router.