Cannot launch Cobalt Demo

Cannot launch Cobalt Demo on Ubuntu 18.04.2 with Proton 4.2.5 proton open

• minhperry · 2019-06-20 · Cannot launch Cobalt Demo on Ubuntu 18.04.2 with Proton 4.2.
  I also got this log in /tmp/dump/$USER_stdout.txt [code]
• minhperry · 2019-06-10 · Cannot launch Cobalt Demo on Ubuntu 18.04.2 with Proton 4.2.
  At the first time launching with `PROTON_LOG`, the poped-up window stayed for very long (~2min) and then disappear. I tried clicking the Play button numbers of times but there are no logs generated. I tried both ~=1 and ...
• kisak-valvemaintainer · 2019-06-10 · Cannot launch Cobalt Demo on Ubuntu 18.04.2 with Proton 4.2.
  Hello @infrustrationMC, the `PROTON_LOG` env variable tells proton to generate a log in your home folder so we can get a general idea of what's happening with the game. Please drag and drop the generated $HOME/steam-4419...