If you're using a USB adapter on a Pi 4 you can use raspi-config to enable booting from an external drive and not worry about SD cards at all
For anyone trying this with a Pi older than the Pi 4, you might still need an SD card with one file on it: https://www.raspberrypi.com/documentation/computers/raspberr...
For anyone trying this with a Pi older than the Pi 4, you might still need an SD card with one file on it: https://www.raspberrypi.com/documentation/computers/raspberr...