These are the following steps I get RDR2 to run using Steam’s proton on Ubuntu 20. I have Intel CPU and Nvidia GPU. (Drivers 460.32.03)

I started by following this guys directions.

Using this launch command: WINEDLLOVERRIDES=dxgi=n,b PULSE_LATENCY_MSEC=60 %command% -adapter 1 -vulkan -width 1920 -height 1080 -USEALLAVAILABLECORES -cpuLoadRebalancing -ignorepipelinecach

I needed to create the system.xml file in SteamLibrary/steamapps/compatdata/1174180/pfx/drive_c/users/steamuser/My Documents/Rockstar Games/Red Dead Redemption 2/Settings/

Using this tool: to generate the file.

After a moment when the game seems like it should have launched I use this command in terminal: PID=$(pgrep RDR2.exe); kill -s SIGSTOP $PID; kill -s SIGCONT $PID

At first launch I had a Rockstar activation error. After launching the game 5 or so times its finally worked.

Now the online version of the game wont connected. I will update that when I figure it out.