How do I migrate The Sims 4 to a new computer?

@BeeboBrink This is the way to do it.

One thing to note is that on most new Windows machines the Documents folder is managed under OneDrive and sometimes OneDrive can make a mess of your Sims 4 folder in Documents.

You options to manage this is one of the following;

1. Always disable OneDrive from functioning while you are playing the game. This solves a good deal of the issues, but not all of them

2. Configure OneDrive to not sync the Documents folder and ensure that the Documents folder is moved to another location on you hard drive and that the windows OS recognizes that the new folder is the official Documents folder. Instructions can be found online via your search engine

3. Uninstall OneDrive entirely from your new PC if you don't make use of it, Problem solved

@BeeboBrink  The above covers things in general, but I want to mention a couple of details in case they happen to matter to you.  First, I'd suggest zipping the folders before transfer (right-click and Send to > Compressed file) to keep them from getting corrupted.  Saves should be fine anyway, but mods sometimes are not.  You may also want to transfer the Tray folder, which holds your saved households and builds.

Second, please make sure you're installing Sims 4 somewhere that is NOT in Documents.  The default C:\Program Files\EA Games is fine, as is a custom folder.  But you don't want the program files and user files mixing—that can only lead to problems.