@XxProShahMeerxX You'd probably need to manually copy over the relevant files from the trial to the full version of the game, but yes, this should work with a Steam install the same way it does with an Origin install. Look in Documents\Electronic Arts for a folder labeled "The Sims 4 Trial" or similar. Inside should be a Tray folder. The files inside that folder are what you need to copy.
Once you launch the full game for the first time, you'll see a "The Sims 4" folder inside Documents\Electronic Arts. Inside that will also be a Tray folder, and you can copy over the files without doing anything else. Make sure those files are just in Tray, not in a subfolder (or inside a Tray folder that's inside another Tray folder).
You didn't ask, but I did want to mention that playing through Steam still requires you to run Origin in the background as well, and to link your Origin and Steam accounts. This is sometimes more trouble than it's worth, and it doesn't necessarily save any money either, since Origin and Steam tend to have equivalent sales a few weeks apart at most. So you might have a better overall experience buying through Origin.
