Hello. I understand you are having connection drops when using your iPhone as a modem via USB. Did you already update both your iPhone and Windows 11 to the latest version? Make sure iTunes or Apple Mobile Device Support is installed so Windows recognizes the USB network adapter.
Open Device Manager and update the driver for your iPhone under Network Adapters. Disable and enable the adapter in Network Connections to reset it. Toggle Personal Hotspot off and on from your iPhone and reconnect.
Check if any VPN or firewall software blocks the tethering. Reinstalling the Apple USB driver often fixes the IPv4 and IPv6 disabled status on Windows 11.
Let me know how it goes.
Regards,
Arlene D.