From Steam, Creeping Deck Demo, The Last Campfire Demo, and Spiritfarer Demo are not imported at all. From Epic, Crying Suns Demo was uninstalled but remains in the Installed/Yes view... except it just vanished from there after I inspected it..?
The two titles that are imported but don't show, one each from Steam and Epic, are games which I also own on Amazon. Instead of allowing me to play them via <ctl-P>, there is a "Play version..." menu (andf also with only one version in it. For each, there is a menu option to install, clicking these brings up the Amazon Games app.
Some of this I just figured out, but at least we have some idea what's going on now.
There is another game I own on both Epic and Amazon, but neither version is installed. Clicking Install on his starts the install process on Epic. Isearched and found a game I own on both Steam and Amazon, clicking Install on this starts the insttall process on Steam. It is possible to install the Amazon versions, as a second level option.
Please let me know if you need any more information.