Go to your Destiny 2 installation folder in your Steam library. The easy way to do this is right click Destiny 2 in Steam, and select 'properties'. In the properties window, go to the local files tab, and select 'browse local files'. Once you have your file explorer open on your D2 install, push ctrl-f and type 'steam_appid' If this file exists, delete it. If it doesn't, get back to me. If it's there, and you delete it, then go ahead and verify integrity of D2 game files in Steam, then try to run it. If you have any more problems, let me know.