I tested this on a pico running MP 1.23 and the latest release of usb-device-cdc.

boot.py:

import usb.device
from usb.device.cdc import CDCInterface

IFACE_TWO = CDCInterface()
IFACE_TWO.init(timeout=0)
#usb.device.get().init(IFACE_TWO, builtin_driver=True)

main.py:

from time import sleep_ms

def main():
	while True:
		print(IFACE_TWO)
		sleep_ms(1000)

if __name__ == "__main__": main()

Running this as-is, IFACE_TWO does show up in main.py, but uncommenting the init function causes the process to error out. This discord post suggests you can call usb.device.get.init() in boot.py, is this no longer true?