Found a solution while searching relative to Darkplaces: Help! DarkPlaces resolutions above 1280x720 only render the upper-left quadrant of the playfield. :: Quake General Discussions
click with right mouse button on .exe file(s) of the game, select
“properties”, go to “Compatibility” tab, check the checkbox named
“Disable display scaling on high DPI settings”.
So, the problem is that I run DPI scaling on my laptop due to its screen being high res but relatively small. Turning off DPI scaling for specific EXEs (like darkplaces and ioquake3) seems to solve the problem.