Simple steps to use with https://firmware-selector.openwrt.org to generate an OpenWrt image for Raspberrypi with Wifi enabled and network over usb (g_ether).
Packages:
# USB Gadget over USB-C
kmod-usb-gadget kmod-usb-gadget-eth kmod-usb-dwc2
# Expand root filesystem to whole sdcard
parted losetup resize2fs