LTSC 2019 Users Cast Aside??

Some features in LrC require  version 1909 (build  18363)  of Windows 10,. This started at version 10. Both Apple and Microsoft have added capability's in their Operating Systems that they do not go back and add to older OS versions.

Another more tech savvy member may list them. As Adobe modifies the programs, they eventually have to abandon support for older OS not having various capability's as to make LrC, etc, run better. 

One factor could be Adobe knows the number of Lightroom users using LTSC is probably extremely small and not worth the investment to test and support.

Not sure how running LTSC equates to being light, snappy & intrusion free, but no need to argue that here. Regardless of your reasoning, I'm afraid you can't run LTSC and expect new stuff to work. That's not what it's meant for. It's a 3'ish year feature lock for stability and to reduce the rate of change if/when you need to keep everything the same. Wanting to hold your OS in place while also expecting to use new apps that are being developed to take advantage of new features isn't realistic. Microsoft makes that very clear too.  Windows 10 Enterprise LTSC - What's new in Windows | Microsoft Docs

"The Long-Term Servicing Channel is not intended for deployment on most or all the PCs in an organization. The LTSC edition of Windows 10 provides customers with access to a deployment option for their special-purpose devices and environments. These devices typically perform a single important task and don’t need feature updates as frequently as other devices in the organization. These devices are also typically not heavily dependent on support from external apps and tools. Since the feature set for LTSC does not change for the lifetime of the release, over time there might be some external tools that do not continue to provide legacy support."

In the end, it's your choice whether to walk or hop on the bus, but if you do decide to walk, you shouldn't expect the bus to wait for you.

Is there any tecnical reason whatsoever to do with the operation of Lightroom that would demand that 1909 is the bare minimum, I strongly suspect not!!

I strongly suspect there is a technical reason.

What do Win7/8 users do for goodness sake if current version W10 users are getting this much of a rough ride?

They can't use Lightroom Classic 11 anyway.

Such narrow compatibility is only going to damage the subscription base, surely?

Doesn't seem that way. Adobe revenue from subscriptions seems to keep rising.

It appears that Adobe have decided that us LTSC users are to be thrown out of the club with the latest upgrade to Lightrroom V11.

No one is throwing you out of a club. You are making a choice to not join.

As far as I am aware Microsoft no longer provides support for Win 7 and 8. That probably means no further security updates.