To be clear, from the command line we can use USB attached drives for temporary use during backups. That does work reliably, though individual configurations can be problematic, (like some USB drives run burning hot during scrubs because they have no fan).
But, Captain Morgan is right that USB attached drives for normal data pools is problematic;
This subject has been coming up quite often in the last year or 2. Perhaps because of TrueNAS SCALE has brought forth some attention to TrueNAS in general and ZFS in specific. Please note that this is about USB attached storage for ZFS data...
www.truenas.com
This is not meant to stop you from using an USB attached drive for data pool usage. It is to warn you of potential problems, (that perhaps you may never experience), and then let you know that if you have problems, we may not be able to help. Other than to say, use SATA, SAS or NVMe drives.