Re: How to use the gallery offline

@Darklo279  Anything you've uploaded to the Gallery, as in, the online feature anyone can access, should be accessible from your new computer.  Anything you've saved to your personal in-game library will be in Documents > Electronic Arts > The Sims 4 > Tray.  So you can transfer the Tray folder from your old computer to the new one, and your content should show up.

I'd suggest zipping the Tray folder before moving it, then extracting it on the new computer and moving the files inside to the new Tray folder, not reusing the old Tray folder itself.