best notable on the backwheel of the bike. did i mess up the settings? any hints?

cheers

It's an ultrawide resolution thing. Happens in all games not fully supporting those resolutions.

Whenever I play at 7680x1440 (3x 2560x1440 in Nvidia Surround), objects become WAY more stretched towards each edge on both the right and the left monitor.

And no, there's nothing you can do about it.
...Apart from abusing the "feature", if you can. If the image is stretched enough with your resolution, you can use it to see around walls or even have the camera completely glitch through buildings.

Just position yourself in such a way that the camera is at the edge of a corner, and rotate it closer to the edge. The camera will either just come closer to you (meh), or glitch through. ;)