Method:
First, gamesaves are located here:
%USERPROFILE%Saved GamesQuantic DreamDetroit Become Human
Then just rename the Detroit Become Human folder to ‘Detroit Become Human.User’.That way you can keep track of whose is whose in the case that you share the game with someone, and the game wouldn’t find it. Then when someone is going to play, they’d just change the folder name back to the default.
Be careful, if you have the “Steam Cloud” option active for this game, It will create a new Detroit Become Human folder with all your last progress again, so just turn it off and that’s it.
Source:
How would one make multiple saves for the PC version? from BecomeHuman
Thanks to utesred!
