External Application??

@aleahjo1  When you download Sims 3 onto a Mac, you download an installer than then runs, as opposed to Origin itself handling the install process.  When the game is downloaded, hover your mouse over the download manager in the lower left corner of the Origin window to expand it, then click the very small Install button.  Origin will show you a page with your product key—be sure to write it down—and then launch the installer.

If you get an error message at any point, please post a screenshot.

What installer do I get?? Other than origin?? 

When I press install after the pop up 

“

1.copy your product code 

product code XXXXXXXXXX

2. install through an external Application 

“ 

the phot connected is the error pop up. What do I need to do , download another application to install?? Or can I get a USB dvd drive and do it that way?? 

Do I have the same problem? So sad :'(

I would love for you to elaborate on the last two options! Please and thanks!! 

@aleahjo1  If you have the storage, you can install Windows alongside macOS on your computer.  For Bootcamp, you use Apple's built-in software to partition your hard drive and install Windows on one side.  Then you boot into Windows when you want to play, and back into macOS for everything else.  With Parallels, you open the app and run Windows alongside macOS.  The disadvantage here is that your Mac has to split resources between both OSs, whereas with Bootcamp, it's only running one at a time.

It can be inconvenient to have to reboot when you want access to Windows, and that's one of two advantages of Parallels.  But Parallels uses its own drivers, which aren't very good, as in, your game will run worse than it should.  Apple offers special Bootcamp drivers that work pretty well.  The other advantage of Parallels is that it requires less free storage.  For Bootcamp, you'll need something around 100 GB minimum to devote to the Windows partition, plus however much free storage you'd want available on the macOS side.  With Parallels, the two OSs would share resources.

It should also be noted that in either case, you'd need to buy a Windows 10 license, and with Parallels, there's also an additional subscription fee.

If this doesn't appeal to you, the other option is to install Mojave or earlier on an external drive or USB.  You'd need temporary access to a Mac running Mojave or earlier—a Mac running Catalina won't run the Mojave installer.  But once you had the OS set up, you could use it on your own Mac, plugging it in and booting into Mojave to play.  Here's a guide:

https://bluebellflora.com/running-32-bit-apps-after-macos-mojave/

I've Bootcamped my Mac and installed Mojave on an external drive, and both were surprisingly easy.

@SuzieMagoozie  I don't think you have the same issue, unless that's not the screenshot you meant to share.  What operating system does your computer run, and what are you trying to do?

Okay so i factory reset my Mac back to Mojave, I’m gonna try to get my sims on here once it finishes, If not I will be back XD

This doesn't really make sense to me. I have played the Sims 3 on my mac for several hours before, until suddenly this has just happened.