For AMD users having issues with non-OpenGL games

Vulkan requires the amdgpu driver, it doesn't detect the graphics adapter when using radeon.

If you're experiencing crashes or the game doesn't load at all, it's probably because your distribution defaults to the radeon driver and Vulkan may be using Intel's graphics adapter instead (if available).

If that's the case, amdgpu has to be enabled explicitly in the kernel commandline.

Instructions for Debian/Ubuntu

Open your terminal and run sudo nano /etc/default/grub.

Append to GRUB_CMDLINE_LINUX_DEFAULT:

radeon.si_support=0 amdgpu.si_support=1 if you have a Southern Islands card.
radeon.cik_support=0 amdgpu.cik_support=1 if you have a Sea Islands card.

For example: GRUB_CMDLINE_LINUX_DEFAULT="quiet radeon.cik_support=0 amdgpu.cik_support=1"

Note: You can safely append both variants if you are unsure which family your card belongs to.

Save with CTRL+X followed by Y and then Enter.

Run sudo update-grub and then reboot your system.

You can check which driver is loaded by running lspci -k:

01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Hawaii PRO [Radeon R9 290/390]
        Subsystem: PC Partner Limited / Sapphire Technology Hawaii PRO [Radeon R9 290/390]
        Kernel driver in use: amdgpu
        Kernel modules: radeon, amdgpu

If your desktop environment doesn't load, check the kernel log by running sudo dmesg. If you see that amdgpu is crashing, append amdgpu.dc=0 to the kernel commandline.

Instructions for Arch Linux

https://wiki.archlinux.org/index.php/AMDGPU

Instructions for Gentoo Linux

https://wiki.gentoo.org/wiki/AMDGPU

If you're still encountering issues

Write a message in https://github.com/ValveSoftware/Proton/issues/813.