1. Local Network permission
Discovery uses mDNS on your Wi-Fi, which iOS gates behind a permission. Check Settings › Privacy & Security › Local Network and make sure Threadlytics is enabled. If you tapped “Don't Allow” at first launch, this is the fix.
2. Same network as your border routers
Your iPhone must be on the same Wi-Fi network as the border routers (HomePod, Apple TV, or third-party hubs). A phone on cellular, a VPN that tunnels local traffic, or a different SSID/subnet will see nothing.
3. AP isolation and guest networks
Guest networks and “AP / client isolation” deliberately block devices from seeing each other — mDNS can't cross that wall. Move the phone to the main network, or disable isolation for it.
4. Do you actually have a Thread border router?
Not every smart-home hub is one. HomePod (2nd gen), HomePod mini, and Apple TV 4K (2nd gen and later) are border routers; many Wi-Fi-only bridges are not, even from the same brand. If you're unsure, the packaging or spec sheet will say “Thread border router.”
Then rescan
After changing any of the above, run a scan from the Overview (tap the freshness row) and give discovery a few seconds. Border routers appear on the Network tab under Meshes.
Checked everything and still empty? Contact support — include your router model and whether other mDNS apps (like AirPlay pickers) see devices.