Could you please check the following:
1. Check your WiFi router settings if it has client isolation enabled.
This setting prevents direct communication between connected devices/computers.
2. Do you have VPN (Virtual Private Network) active? If yes, please disable it.
3. Check on your iOS Viewer Settings -> Privacy -> Local Network, if spacedesk is on the list and enabled?
For assistance, please also refer to the Troubleshooting -> Network Connection chapter in the user manual https://www.spacedesk.net/user-manual/#item_489.