I asked ChatGPT about it since I’m not sure how to go about it, and got this. Might be worth a try.

Prompt: In a recent update to the fedora operating system they changed it so mobile broadband modems are now flagged as WWAN devices rather then ethernet devices. This is causing it to treat a usb tethered phone as a WWAN device instead of a ethernet over usb device, and the tether is not working as a result. How could a user fix this on their system?

Answer: You can teach ModemManager to completely ignore your phone’s RNDIS interface so that NetworkManager will handle it as a normal Ethernet link again. Here’s how:

1. Find your phone’s USB IDs
   Plug in your phone with USB‑tethering enabled and run:

   lsusb
   

   You’ll see a line like:

   Bus 002 Device 008: ID 18d1:4ee7 Google Inc. Nexus/Pixel (tethering)
   

   Note the idVendor (here 18d1) and idProduct (here 4ee7).

2. Create a udev rule to ignore it
   As root, create /etc/udev/rules.d/99-usb-tether-ignore.rules with these contents:

   # Tell ModemManager to ignore my phone’s USB‑tether interface
   ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="4ee7", ENV{ID_MM_DEVICE_IGNORE}="1"
   

   (Replace 18d1/4ee7 with your phone’s IDs.) citeturn5search4

3. Reload udev and restart services

   sudo udevadm control --reload-rules
   sudo udevadm trigger
   sudo systemctl restart ModemManager NetworkManager
   

After that, your tethered phone will no longer be treated as a WWAN modem but as an ordinary USB‑Ethernet device—DHCP will kick in and Internet will flow as before.

Tip:
If you never use a cellular modem on this machine, you can also just uninstall ModemManager entirely:

sudo dnf remove ModemManager
``` citeturn5search4