You will need to open the library part and then add the image you want to see for the file icon in the "Preview" dialogue window.
Let me know if you need a screen shot of where to go - I don't have Archicad running at the moment.
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