How to Run the game at Screen refresh rate in Fullscreen
The game ignores Windows settings and forces 60 Hz while in fullscreen as long as it’s supported by your monitor.
While originally intended for Mafia III, it works for Mafia: Definitive Edition too
Run at default monitor refresh rate with this Mafia III ReShade custom build
Download ReShade Mafia III fixes (dxgi.dll).
Copy the file to the installation folder.
When going fullscreen, the game will run at whatever refresh rate you currently have by default.
This supports anything ReShade supports.