Can you please check if Proton 3.16 Beta is installed under the Tools tab of your library?

It is indeed.

Weird thing is on my other machine, it works.
The machine erroring out has the Steam library on an NTFS drive. It runs other games from there fine (native)
I tried uninstalling the tool but it complains about "missing shared context" (Even on the machine that works)
Hello @parkerlreed, using Proton on NTFS is known to be problematic https://github.com/ValveSoftware/Proton/issues/82#issuecomment-415099440. Please give #11 a read.
Ahh thanks. I could have sworn this was working for a while. Just coming back to this after finally resizing NTFS down to less than 2TB free... https://github.com/ValveSoftware/steam-for-linux/issues/5742
Honestly at this point I'm done. I'll just move everything over to EXT4. Thanks.
proton 3.16x2 2019-03
Compatibility Report
System Information
I confirm:
Symptoms
Whenevr I try to launch any title using the latest beta, I get this error. z: folder does not exist.
Reproduction
Launch any title with newest beta