Many thanks Mark; although both use .Net Core 3.1 the new updater is a desktop application, whereas Web Display is a console application, hence the reason for the different runtime library. I spotted the runtime requirement when testing Web Display on a different system, but didn't myself see the message for the new updater as my test system must already have the required library installed.I eventually sorted it out. Google is your friend! In my case, I had to install the Microsoft Windows Desktop Runtime - 3.1.28 (x86), not the dot net-runtime-3.1.28-win-x86.exe.
Thanks again for the correction,
Martin