Hi! it's a weird Mac issue. I've got a solution here: https://steamcommunity.com/app/1566070/discussions/0/3800526843213036679/
This is what popped up I tried following the troubleshoot steps this is from steam.Hey again! I did a little research and found this information from Steam : https://help.steampowered.com/en/faqs/view/3A2A-BF2D-15FF-7963
This error is generally due to one of two things: 1) anti-virus is blocking your game launch or installation; 2) an incorrect delivery of the game files by the Steam service.
Start by disabling your anti-virus software before updating/running the game.
If that doesn't work or you don't have anti-virus, please validate your files, by right clicking on the game title in the Library of the Steam client. Then pick: Properties > Local Files > Verify integrity of game cache.
Secondly, right click the game in your list and "delete local content". Then, reinstall your game, preferably to a different drive or folder if available. Please ensure you have enough local space to install and run your game.
If that doesn't help, please try:
1. Completely exit Steam.
2. Navigate to your Steam installation folder (~C:\Program Files\Steam)
3. Delete the 'appcache' folder.
4. Restart your computer and attempt to launch the game through Steam