Aravisian,
Well, I appear to have a Zorin 16 Pro system up and running alongside Windows 10 on my Dell Laptop 
am writing this in Firefox on Z16Pro....yabbadoo.
The grubx64.efi file was on the Balena flashed iso and so I could add Zorin as a boot option as per the Zorin guys fix. Strange that the grubx64.efi was not present when flashed by Rufus.
Anyway, all done. Dual boot to Win 10 works.
One quick question, once I check out the things I need to I'd like to get rid of Win 10 and just have Zorin on this laptop. Would that simply be a case of running the install routine again and selecting the option to wipe everything and install Z16Pro afresh?