[dubster]

Is the usb stick formatted as portable?  If it's not, Kodi won't see it.  Also, see if Kodi's log has any info after you attempt a start-up.

Not sure if its formatted as portable, but Kodi can definitely see it as I can browse to the usb stick from within Kodi. 
Cool, ok I'll take a look for the log file tomorrow.

 This link explains portable vs internal formatting:  https://bit.ly/3fBKtCU

Thanks - that looks like SD rather than USB.  And the method for doing it doesnt look like a fire TV thing either.
Since Kodi can see the drive and play videos off it Im assuming it must be fine.