EA Play is a subscription service. Are you saying you originally subscribed to EA Play on Origin and now have it on the EA App? If so no DLC you got thru your EA Play subscription will be available on Steam.
If on the other hand you wrote EA Play by mistake and meant the EA App then make sure that you have linked your Steam account to the EA account where you have the DLC.
Try to unlink the accounts then link them again and see if that works. Perhaps Steam support can help. You can also try to contact EA Support. https://help.ea.com/en/contact-us/?product=the-sims-4&platform=pc&category=technical-support
@ashleypopay Linking accounts doesn't make EA App-owned packs appear in your Steam library. You'd still need to download those packs from the EA App, and their data will go into the program files for the Steam install and allow those packs to load in-game. Just make sure you're not downloading a second copy of the base game, or those packs may install into that second copy and not into your Steam install.
If the EA App thinks your packs are installed but they're not loading in-game, please see the first post of this thread:
