If I remember correctly, I used ApplePiBaker (on OS X) to make a backup of the SD card as a image/or zip file on the mac and then ran it again to copy from the backup and install on the SSD (wiping it out completely is part of the process). I plugged in the SSD into the RPi4, removed the SD card, and powered the RPi4 up.

There is equivalent software on Windows, but I've forgotten the name.