How can I fix no cellular network on iPhone after iOS 18.4.1 update?

Try this:

1. Enable Airplane mode
2. Wait 30 seconds then turn Airplane mode off.
3. Restart iPhone.
4. Test network.
5. Still not working, try reset network settings.
6. Report back if still not working.

Would be good to know if you are using an eSIM Or not. Here are instructions

on how to reset network settings.

Reset your network settings, tap Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings.

Take note that this also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.

Cheers

Remove all add-on “coffee shop” VPN clients that might be installed, restart, and test again.