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. Are you using any third-party antivirus/firewall? if yes, please add spacedesk in the exception list or ‘Allow List’
4. Check on your iOS Viewer Settings -> Privacy -> Local Network, if spacedesk is on the list and enabled?