I believe it is a video card / driver issue.
We had similar problems back in version 17 - some machines had this problem while others were fine.
There was a hotfix that supposedly addressed this problem (see attached image).
Check you have the latest version of Archicad.
Check you video card drivers as well.
We are using the latest build for 18 and I haven't had any complaints about this lately - but we have also changed our machines as well.
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