Re: how to transfer purchases from a mac to windows

@BayleeBasically  You don't need to transfer your purchases: they belong to your account, not your computer.  So just sign into Origin or the EA App with the same email address and password you've been using on your Mac, and you'll be able to download all your content again, for free.

By the way, you can in fact transfer your saves to your new computer.  They're located in Documents > Electronic Arts > The Sims 4 > saves in both operating systems.  It would be best to zip the saves folder, or at least the saves you want to keep, before transferring.  (Right-click and select Compress in macOS.)  You can move the .zip to a USB stick that's compatible with both OSs, or you can upload it to a free filesharing site (Google Drive, Dropbox, etc.) and download it on your new computer.  Right-click and select Extract to extract the files in Windows.

The same goes for the contents of the Tray folder, which contains your saved households and builds.