Adding a reproducible recipe for anyone still stuck, since the two workarounds mentioned above each have a missing piece that cost me time. First, one more confirmation that this is device-wide and not app- or signing-specific: on my watch (26.5.1), App Store apps (Snapchat, American Airlines) fail to install exactly the same way as my own dev build — about a one-minute spinner, then "could not be installed at this time." In my case reboots, unpair/re-pair, and the Bluetooth off/on toggle on both devices did not help (glad the toggle worked for some above — it didn't take here). TestFlight fails too, same transfer path. What worked, reproducibly: Turn the iPhone's Bluetooth OFF and leave it off. This forces the watch onto WiFi and lets the Mac-to-Watch CoreDevice tunnel come up. In my case the tunnel had been dead for about a day (tunnelState=disconnected, ddiServicesAvailable=false) and only came up once phone Bluetooth was off. Keep Mac, iPhone, and watch on the same real WiFi network — not the iPhone's Personal Hotspot, which isolates the devices from each other. Install from the Mac with devicectl, not Xcode "Run": xcrun devicectl device install app --device WATCH-COREDEVICE-ID --timeout 240 "~/Library/Developer/Xcode/DerivedData/YourApp/Build/Products/Release-watchos/Your Watch App.app" (Get the watch's CoreDevice ID from: xcrun devicectl list devices. Use the Release-watchos build product — it's clean, no __preview.dylib.) Two verification gotchas that make this path look broken when it isn't: devicectl device info details can keep reporting tunnelState=None from stale cache even when the install succeeds. Trust the "App installed" output of the install command, not the info query. Xcode "Run" stalls at "Copying shared cache symbols (0%)", which returns HTTP 403 on 26.5. That symbol download is debugger support only — it has nothing to do with installing, which is why devicectl works while Xcode appears broken. Caveat: this is dev-tools-only — it doesn't help enterprise end users without a Mac. For them the both-devices Bluetooth toggle above seems to be the only lever until the fix ships. Has anyone on the 26.6 RC been able to confirm whether this is fixed there?