It works, but when renaming the file, you need to leave just “QuantumBreak” without “.exe”. Then Steam won't complain that it can't find the executable file.
In addition, when unpacking, I checked the “Keep blind section” box. I don't know if it's necessary or not, but that's what it says on GitHub. Screenshot

I'm pretty sure this worked for me back in August but now it doesn't.
I set the file to 5120x1440. It defaults to 1280x800. I've tried with and without Hydroculator's suggestion. 7900xt; G9 OLED

works at 3440×1440 but could not get 5120x1440 unfortunately

I got this to work on a 5120x1440 monitor in 2025.
There's two important changes to this guide that I needed to make it work.

1. In the steamless app, check the "Keep Bind Section".
2. Don't try to run the plain executable. For some reason, this does not work. You need to have the exe with the original name, and run it through Steam. When I tried to run the exe manually, it would go black for a second then crash, no messages or warnings. But running through steam after updating the ini file worked perfectly.

Used Steamless v3.1.0.5

For reference, this is where I found the bit about the additional steps:
https://github.com/atom0s/Steamless/issues/105

Latest comments are saying it's not working, so just leaving a comment here confirming that it worked for me. 3440x1440.

Doesn't work... and seems I'm not the only one it hasn't worked for.

Tried this for 5120x1440 on my G9 OLED, no dice. Gave an error about storage device and reverted back to 192x1080... Yes, I did remember the rename step... lol

Just wanted to confirm that this does still work. Thank you for the guide! Make sure you unpack your exe with the Steamless tool, the patcher will not work if you don't do that.

Followed the steps, but after running the Steamless unpack, the exe simply opens to a black window and closes without a error :(

application load error 3:00000065432 didnt work for me