If you are on Linux and are currently experiencing issues launching games, please check your game log ("Report a problem running this game" on the game details page). If the log file contains "TypeError: Use delete() to clear values", you will have to temporarily disable umu (in the "Advanced" category of the game settings)
There is an issue with the umu API at the moment. It should hopefully be resolved in a few hours
This issue is now resolved. Please un-check the "Disable umu" checkbox if you checked it because of this