What is happening (tested on default cube)
Alt + Left Click does NOT select an edge loop
Select → Edge Loop (menu) also does NOT work
Loop Cut (Ctrl + R) inner loop selection works
Edge Ring selection (Ctrl + Alt + Click) works
Selecting edges connected on the same axis/plane works
Happens on a fresh default cube, no extra geometry
What I have already tried
Tested on Blender 3.6, 4.5 LTS, and 5.0.1
Changed mouse (hardware test)
Checked Emulate 3 Button Mouse
Reset preferences to factory defaults
Verified Blender Default keymap
Disabled Xbox Game Bar and Windows overlays
Disabled NVIDIA in-game overlay
Issue started recently (was working earlier)