I use two different Mac devices to play Sims 4

@AggsFan  Your saves are stored locally on your Mac, specifically in Documents\Electronic Arts\The Sims 4\Saves.  To use the saves from your laptop on your iMac, you'll need to manually transfer them.  In fact, you can copy the entire folder over to the iMac if you want.

One way to do this is to use iCloud, since you can sign in on each computer and pull the folder to your hard drive when you're ready to play.  But if you do use iCloud, make sure it's not set to automatically sync your Documents folder.  That often causes saves to go missing, plus in this case, you wouldn't want the older Sims 4 folder overwriting the newer one.  Here are some screenshots of how to manage your iCloud settings:

https://bluebellflora.com/2017/02/06/sims-3-and-sims-4-not-loading-save-games/

You could also use a free filesharing site to transfer your saves, or your whole game folder.  Right-click (or hold the crtl key and click) on the folder you want to move, select Compress, then upload the .zip file.  When you download it again, double-click to unzip, and place the folder.