Note: This is an update of Will Haley's excellent post to use APFS instead of CoreStorage.
The script can't read the file containing the password on the USB thumb drive. When formatted
as FAT32 as described below, the user/group of the file is unknown/unknown. But I also tried formatting the USB thumb drive in HFS+, unchecking "Ignore permissions on this volume" and changing the file owner to root:wheel
. The file is still not readable to the boot process. Probably something to do with new security restrictions in Catalina. A script running as root reading data from a thumb drive? Makes sense.