Hello, we (PCSX2 Team) recently discovered that anisotropic filtering doesn't work on OpenGL in any situation on windows. The issue was also reproduced by our testers.
Here are image comparisons between intel igpu and amd dgpu amd r7 360
Something to note that one of our contributors is using legacy(2015) drivers with a legacy gpu and aniso works for him on those old drivers.
Note: I'm running an older driver however issue is also reproduceable on latest one as well.
Test case should be run with both MIN(F1) and MAG(F2) set to Linear, aniso can be toggled with F3.