ISSUE
If you install your games outside the directory your steam is located (like many people do) and this directory happens to be ntfs format, the game will fail to launch.

OS:
Kernel: 6.14.0-29-generic arch: x86_64 bits: 64 compiler: gcc v: 13.3.0 clocksource: tsc
Desktop: Cinnamon v: 6.4.8 tk: GTK v: 3.24.41 wm: Muffin v: 6.4.1 vt: 7 dm: LightDM v: 1.30.0
Distro: Linux Mint 22.2 Zara base: Ubuntu 24.04 noble

STEPS
Install non linux-native game (Deadlock in my case) into a ntfs directory/partition seperate from your local steam installation
Attempt to launch the game

FIX

I searched long and hard, as I am new to linux, reviewing my drivers and versions of proton so i can confidently say that the issue lies with protons ability to mount paths,
A fix I found after a few days and the reason I could fix this issue for myself can be found in the github comment link below, posted by the user PandorasFox on May 16th.

https://github.com/ValveSoftware/Proton/issues/5168#issuecomment-2887824352