DIAGNOSIS The printer's mDNS (Bonjour/AirPrint) service has crashed. This is a common firmware bug after a network change.
FIX Restart the printer's network stack. On the OLED screen, press Setup. Go to Device settings > LAN settings > Wireless LAN setup. Select Yes to reset the LAN settings. The printer will restart its wireless module. Reconnect your phone to the same 2.4GHz Wi-Fi network as the printer. Try AirPrint again.
IF THAT DIDN'T WORK Your router may have updated and enabled AP Isolation or a client firewall. This blocks device-to-device communication. Disable these features in your router settings for the printer's connection.
HEADS UP Canon PRINT app is more reliable than native AirPrint for this model. If AirPrint fails, use the Canon app as your primary print driver for mobile.