With PROTON_USE_WINED3D the game works flawlessly.
Using Vulkan with logs enabled it shows the following error:
21996.148:0036:0037:fixme:vulkan:X11DRV_vkCreateWin32SurfaceKHR Application requires child window rendering, which is not implemented yet! err: Failed to create surface
Complete log attached, proton 5.0.6
steam-506260.log
Obligatory reference to https://bugs.winehq.org/show_bug.cgi?id=45277.
proton 5.0x1 2020-04PROTON_USE_WINED3Dx1 2020-04
Compatibility Report
System Information
LOG:
steam-506260.log
Symptoms
When launched, window is filled with window manager garbage. Nothing is rendered. I had to force quit.