Most of the time when I notice poor font antialiasing it's due to the OS resolution or subpixel antialiasing not precisely matching the panel. An old OS will no

Most of the time when I notice poor font antialiasing it's due to the OS resolution or subpixel antialiasing not precisely matching the panel. An old OS will not have subpixel antialiasing, so if it looks correct you could try disabling subpixel/ClearType, or testing a bitmap font. If the old OS still looks wrong, your panel may be pretending to be 4k and actually stretching things a little. Also, any OS level scaling is likely to mess with things, so check that it's either 100% or 200%.