macOS 10.15,4 latest Steam;
After installing the game on a secondary location, on an external drive as configured by Steam, the app cannot be launced with the PLAY button. Error alert shows: "An error occurred while updating WFTO (unknown error)". So apparently a necessary update cannot happen.
Solution: Move the game installation (via Game Properties) to the regular Steam location in the AppSupport folder... then launch, it works fine. Afterwards, game can be moved back to external drive and also launches as expected.
Bug = initial installation in an alternate folder in Steam is not possible
Customer support service by UserEcho