Games not no longer start via Steam

gurkenbeast​  Are you trying to launch Sims 4 through Steam or the EA App?  The second error looks like what might happen if you install the game through Steam but try to launch it through the EA App.

Aside from that, please make sure that your Steam and EA accounts are currently linked to each other.  Try to sign into an EA website (this one is fine) with your Steam credentials.  If you land in the correct EA account, they're linked; if anything else happens, let me know.