Think you will need to produce some error logs.

@jarrard could you please assist? what log would they need and how would you produce them? thanks :)

NTFS is known to have issues on Linux, this isn't really a supported configuration. You might find some help at #35 and #11.

Even if it's not a supported configuration, can there be a FAQ entry about it?

At the very least, proton's (and/or Steam's) error message can be more helpful by detecting the issue and providing some guidelines.

https://github.com/ValveSoftware/Proton/issues/82#issuecomment-415162671

Please check out #35 , specifically my first part where I mention ntfs-3g. Read on further in the issue for help if more file permission errors occur.

https://github.com/ValveSoftware/Proton/issues/35#issuecomment-414935724

Thanks for sharing my fix, aeikum!

It's a problem with proton and the names of some directories contained in the wineprefix created for each game when both resides in a NTFS formated partition.

I commented it in https://github.com/ValveSoftware/Proton/issues/82#issuecomment-415099440

Those who change permissions to the drives might get a popup on launch to enter password for mounting your internal drives. A solution for me with KDE5/Arch setup is below.

First be sure your part of group storage with: useradd -G storage USERNAME

Second make a file in /etc/polkit-1/rules.d/ called 10-mount-system.rules:
ie. sudo gedit /etc/polkit-1/rules.d/10-mount-system.rules
(I use gedit because.. but nano or anything will do fine)

Put the below text in the file and save+reboot, it should no longer ask for password to mount drives on desktop launch.

polkit.addRule(function(action, subject) {
     if (action.id == "org.freedesktop.udisks2.filesystem-mount-system" &&
          subject.active &&
          subject.isInGroup("storage")) {
          return polkit.Result.YES;
     }
});

Are you sure this is an NTFS issue? I just installed a game, let the Proton prefix creation and dependency installation script complete, confirmed it works. I then moved it to a different library within the same filesystem (ext4) and the game stopped working complaining about missing drives. Then I forced a different Proton version (which created a new prefix) and it was working again (from new location).

I might be entirely wrong but I think some paths in the prefix aren't changed when the game is moved between libraries.

NTFS handling has been greatly reworked from last year till this April.
Whatever this bug was, my 2c would be it's fixed now.

I can reproduce this bug in manjaro. I installed mirrors edge in a ntfs partition, didnt worked in proton (it worked in wine but thats not relevant). So I moved it to an ext4 partition and now it works

1. NTFS requires certain configuration adjustments in the mount options which are covered in the proton wiki (read it!)
2. Proton does not execute well off ntfs drives, that is the proton base install, be sure it's in your .steam folder steamapps on the linux main drive and not installed on any NTFS or external drives (it auto installs to my ntfs if I install proton after adding the ntfs drives).

I fixed this bug, time ago, I would hope this get fixed in steam so it will work properly by default

So theoretically a game installed on an NTFS drive should work with Proton now?

As long as it's mounted with the right options prolly?