I just downloaded your 'Library - Schematic' folder and using the 'ADD' button in the library manager it did indeed add the folder as a linked library with just the one window object in it.
What is the one warning message in your library manager.
That may offer some clues.
Actually I just checked and I have the same warning.
It seems you have managed to copy a window from the Archicad library rather than saving as a new window.
Simply copying and renaming does not change the internal GUID, so Archicad considers them the same object.
Sometimes these duplicate objects will only show one or the other.
I am not sure why I am seeing both and you are not.
But your window seems no different than the 'Vertical multi-sash window 23' - so just use that instead?
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11