@BenganJ - I've directed this at you but have written it for others that may read it, so don't be annoyed if you think i'm telling you something you already know.
Once we had the working AA bit we had to find a fix for the graphics glitch it caused when switching between driving screen and menu screen. We tried changing uset g_menu_aa_limit "8" to different values but it didn't help and so that is the only reason why it's stated in the first post when it's at the game default value anyway.
The proper fix for the glitch being my multimon file.
The game uses SSAA for menus and SMAA for driving.
Time for a test!
I think we should turn off menu SSAA and let our MSAA work it's magic instead.
In ATS garage menu i see a poor image quality... (my texture filtering is 'quality' and not 'high quality').
Here is an image from ATS garage menu, left menu_aa_limit "8" & right menu_aa_limit "0".
MENUAA.png
As the truck rotates it no longer sparkles with horrible chrome and instead is worth my time to admire.
I've switched back and forth between menu/driving/garage(truck config)/garage(trailer config) and waves background and all seems well as long as the multimon file is used.