To my knowing there is no mod and probably never will be. The game UI wasn't designed for 16:9 or other aspect ratios.
I just launched vanilla in 1920x1080p and didn't see any ui stretching.
Do it the other way around. start in 4:3 aspect ratio (like 1024x768) as the game was original meant to be played (~2004-2005) and then you see how it should look.
At least if you switch later to 1920x1080p again, you see the difference
adjusting all the vanilla UI textures in aspect to fit the 16:9 ratio is an option, but that's not what I would want to do. Oh, and that must be done for all race mods as well. The results could look worse then the stretching we see now I can imagine.
Edited by mdcertainty, 24 September 2019 - 11:41 AM.