I had quite huge troubles with starting the game. At first I had to rename launcher as everybody suggested. That led me to constant black screen with splash image shown. To fix that I had to enable Proton logging, dig in log file and find that Proton's Vulkan drivers can properly start, then install Vulkan drivers and use more recent NVidia drivers (390 vs 340). As a result, I could start to play normally with my friend. Although, mini-map lags and disappears after each location loading (press M to open big map and mini-map will fix itself). And if game runs in full-screen mode it is better not to Alt-Tab, otherwise it will freeze or squeeze the resolution/image.