Re: Sims 4 Game Launching Problem: EA Account Replaced Steam Account

@Sawtooth_005  It sounds like you may be signing into the wrong EA account, as in, not the one linked to your Steam account; or that there's a problem with the account link.  To test this, please go to any EA site (ea.com is fine) in a private browser window, click the sign in button, and login with your Steam credentials.  Make sure you land in the correct EA account.  If you don't, or you get an error, let me know.

More generally, you'll still need to launch Sims 4 through Steam in order to access your Steam-owned content.  You should be able to download your EA App-owned content into your Steam install, provided the accounts are linked properly.  But downloading a second copy of the base game is unnecessary and will only confuse the EA App.