[Matt Devo]

I've updated my previous message with corrections after gaining more experience (many hours!): I hope my mistakes will help others avoid this waste of time.
My Chromeos storage manager showed only 1.1GB free, so that's why the Chromebook Recovery Utility (CRU) could not write the image to the USB flash drive.
Using the CRU on a W10 machine worked for me now for all USB flash drives.
...just had to wait much longer letting the CRU write several partitions to the USB flash drive.

the drive showing 1.1GB free shouldn't be a factor. The Chromebook recovery utility writes an image to the USB, complete with partition layout and data. It doesn't care what if anything is on the drive, what format, etc. All that matters is that the drive capacity is large enough to support he image being written.

The sun is shining today.
I reset the partitions: Chromeos showed 10GB (why not 16GB?) before I reinstalled the dual boot with LibreElec (LE).
I gave 6GB to LE, 4GB to Chromeos.

Thank you so much for your quick and precise comments. It helped me persist. 

 
ChromeOS itself reserves 6-10GB for the OS depending on version, model, etc. 10GB is what is available to the user. The recommendation of partition size from the EZ Setup script takes this into account.