The game was originally released exclusively to Epic Games Store and now it's coming to Steam in less than two weeks. I got an early Steam copy through the /r/ultrawidemasterrace curator, which is a bit funny, considering we can't even review it as supporting ultrawide.
What we can do is hack it like there's no tomorrow, right?
I found that the game is built on a very recent version of Unity - 2019.4, meaning that some tools used to unpack Unity assets do not even work on it. I tried a couple of things and also saw that the main code of the game was packed, which is unusual for a Unity game, forcing me to resort to the good old assembly and treat the game as a black box as opposed to reading through its disassembled code in C#.
Some hours later, after experiments with injecting a bit of my own code, I boiled down the solution to just two operations to change, forcing the game to pull the current resolution of the display, not its hardcoded values. It even works in real time if you switch to a different desktop resolution.
The downside is that this will work only in borderless, not exclusive fullscreen.
I could dig deeper and address it (maybe make a trainer that pulls the values from elsewhere) but I don't think it's worth more hours, especially considering that the game has no HDR support contrary to some earlier claims.