Game will not launch after downloading.

MehoyMinoy8  The only way to use Steam-owned content is with a Steam install.

What country are you in?  If you're using a VPN, does it help to disable it?

If that's not relevant, as a test, please create a new admin Windows account and try playing there, still through Steam.  Make the account local, as in, don't link it to your Microsoft account or any email address.  You'll be able to (try to) launch Sims 4 without reinstalling anything.

If that doesn't help either, please post a screenshot of the error you get when you try to launch Sims 4 through Steam, for reference.  Please also let me know whether Sims 1 and 2 work.

Edit:  I've now seen two other threads about this issue, which makes it a pattern.  So please try again to launch Sims 4, then create an EA App error report:

https://help.ea.com/en/help/ea/ea-app/run-ea-error-report/

and post the report ID in a reply here.  I'll pass it along.