The very first time you run Archicad after installing it a dialogue box ususally pops up asking if you want to allow or block internet access.
Maybe this is hiding in the background.
Wait a few moments after starting and then just press the Enter key.
Or try Alt-Tab to cycle through the running applications to see if anything is hiding.
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