It's not just me that the watch doesn't show up in Xcode 15.3, Watch 10.4, iOS 17.4.1, right?
In Xcode, the Mac and iPhone are connected and displayed, but only the watch is not working. And when I run the complication app, oddly enough, it prompts to install the app on the iPhone device's watch app? It's really strange, isn't it? But the installation doesn't actually happen. It seems like a funny thing with Apple. Does anyone know when this will be fixed?
I think that's just you. You need to restart your devices, maybe? Perhaps you haven't enabled Developer Mode?
The iPhone shows developer mode, so I turned it on, but it's not visible on the Apple Watch.
On your Watch, go to Settings > Privacy & Security, then scroll down to Developer Mode, and turn it on.
Returning to the main point, it seems I'm not the only one having trouble connecting Xcode 15.3 with WatchOS 10.4, and it appears no one has found a solution yet.
https://developer.apple.com/forums/thread/747784?answerId=784999022#784999022
Same problem on my side with Sonoma 14.4.1, XCode 15.3, iOS 17.4.1 and watchOS 10.4
FYI - I solved the problem by making sure that all devices (MacBook, iPhone and Watch) are connected to the same WIFI access point.
In a large space with multiple access points broadcasting the same WIFI , it is easy to not have all the devices on the same Wifi on using diifferent APs and this breaks connectivity (probably similar to the problems others have found when using a VPN).
As a workaround, I ended up creating a dedicated WIFI network only on one AP just for my MacBook / iPhone/ Watch => then it works (even if I often have to force the watch to connect to the "right" AP that is technically 2 feet away).
Tiry
