This support links to race online in AC through Content Manager alternative launcher on Linux. You can also add it as non Steam game to launch it from Steam, so you can keep original launcher.
Create script to run CM (Placed in $HOME/Steam/accm.sh
)
#!/bin/bash
export STEAM_COMPAT_CLIENT_INSTALL_PATH=$HOME/.local/share/Steam
export STEAM_COMPAT_DATA_PATH=$HOME/.local/share/Steam/steamapps/compatdata/244210