Hello
Quick follow up to my previous post since the thread was closed after 90 days.
Zorin Pro 17.3 has been installed now to my relatively modern laptop, a device with many bings and twee-hoos <apologies :)> The laptop has an SD card slot which is populated with a 128 GB micro-SD which is now encrypted with LUKS and working well so far.
The difference between the previous machine which failed and the laptop isn't much. My guess, and it is a guess, is the TPM chip on the laptop. The older computer doesn't have a TPM chip which may be what is enabling the LUKS failure. The only other differences are really performance and capacity and the operating system version. TPM chip may be necessary for LUKS to work as advertised.