The method for using guidelines changed in 15.
You now have to activate with the keyboard shortcut and then select the guide you want.
It is possible while in the process of drawing to click-hold and drag the mouse to select a guide line also.
Best to read the manual or check out the youtube movies.
Here is an old post that may help a bit.
http://archicad-talk.graphisoft.com/viewtopic.php?p=194112
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