Like many players, I had issues with resolution changes not applying after launch.
I tried every fix from all the guides across GOG and Steam but to no avail... Until now.
The solution was simple, so I really hope this helps others enjoy The Saboteur in 2024!

Adjusting "VideoSetup.exe" in the game's install folder to the desired resolution, locking the refresh rate to 60Hz or reducing the active CPU core count to 4 has allowed the game to start for some but no matter what I tried, I was always stuck at 800x600 despite editing the "config.ini" file in "Documents\My Games\The Saboteur™\SaveGames".

If this all sounds familiar, I've got good news for you; the fix lies in running "Saboteur.exe" in compatibility mode for "Windows 98 / Windows Me" and then adjusting the new "config.ini" file that is then created in "Users\Public\Documents\My Games\The Saboteur™\SaveGames".

"VideoSetup.exe" in the game's install directory and "config.ini" in "Documents\My Games\The Saboteur™\SaveGames" no longer applies to the version of the game running in compatibility mode for "Windows 98 / Windows Me" and should now be ignored. Your saves will also now live in "Users\Public\Documents\My Games\The Saboteur™\SaveGames" too.

I'm now running 2560x1440 at 60Hz on a Win 10, Ryzen and RTX system.
Thanks for reading and please share with anyone else who's struggling.