The problem is that your screen might not be giving you the best performance if you use a different resolution than the recommended one. Using different resolutions (lower or higher) just might "blur" the screen, making it more difficult to read.
At least, you should try a couple of options, like:
A_ Set the screen resolution recommended by the manufacturer, and the magnifier to 2x or more (meaning, play with the magnifier's settings).
B_ Set a lower resolution than the one recommended by the manufacturer, but
keep the ratio of 1.6 ( 1680 / 1050 = 1.6 ),
instead of changing it ( 1024 / 768 = 4 / 3 ).
My guess is that using the screen resolution recommended by the manufacturer, using Windows "High Contrast" settings and elevating the magnifier you might get better results than lowering the resolution to a different format (like your current 4 / 3 ratio).
BTW, changing the default font size in Windows Control Panel Appearance settings (or Themes), might also influence some fonts in avast (this was recently reported by another user).
Please let us know if any of these options improves your situation.