Ralana2727 Thanks for the dxdiag. Please change the two settings listed in this post from bibliomak:
Sims 4 Crashing/Freezing/Lag, Surface Pro 7 | EA Forums - 11836525
The thread was originally for a different model Surface, but it applies to yours as well.
As for why the EA App is lagging, I don't know. But if the above doesn't help with the App itself, I would uninstall it again and restart your computer, then download a fresh copy of the installer and run it as an admin: right-click and select "Run as administrator." This can help with installation-related issues.