Any idea why iMac does not find Sonoma 14 OS when I click on the "Get" button in the Apple Store? The description states it works with this Mac but does not find it when I try to update. Currently running OS 13.6 on a Retina 5K, 27 inch (2017) iMac.

You need a 2019 or later iMac to run Sonoma. Since your iMac is a 2017 model, it is compatible with Ventura, but not with Sonoma.

macOS Sonoma - Apple

macOS Sonoma is compatible with these computers - Apple Support

With respect to the "Compatibility" indicator in the App Store, I have had it tell me that old apps that I previously purchased for an Intel-based Mac were compatible with my Mac, when in fact, they were not.

FWIW, the App Store is confusing. It will say "Works on this ****" as long as you are running High Sierra or later. Which actually means, you need to be running macOS 10.13 or later to install Sonoma on a compatible Mac. Yours is not.

Ventura will be one of “the most recent three” until the successor to the successor to Sonoma is out. So you have maybe a couple of years (plus or minus) during which your machine can still get the most critical Apple security updates, and during which it will be able to run current applications from the likes of Adobe and Microsoft.

But if what you want is the Sonoma features, and/or an Apple Silicon processor, then I guess it is time for a new toy.

You're welcome.