Cats & Dogs does not run.

isaporta  Please run a search for EP04, which is the folder for Cats & Dogs.  Open a File Explorer window, click This PC in the left panel, and enter EP04 in the search field in the upper-right corner.  Wait for the search to finish, then make sure the full file path is showing under each result.  If it's not, expand the window sideways as necessary.  Take a screenshot using Windows key-shift-S and attach it to a reply here.

I use the EA app to launch and Epic Games. 

Thank you for the reply, and I really hope that you can help me. 

Again, I thank you in advance for your help.

Also, when I open the The Sims file, I cannot find the EP04 folder in there.

isaporta  You have two copies of Sims 4 itself installed, one likely from the EA App and the other from Steam.  Do you want to keep playing through the EA App, or do you want to play through Steam?  If you own any content in Steam, you'd need to use it through Steam, but otherwise, you can choose.

The EP04 folder isn't supposed to be in your Sims 4 user folder (second screenshot), so don't worry about that part.

All my add-ons are on EA itself, not on Steam. So, I guess I'll keep playing through EA.

So, in the end, I just need to make sure that I delete the Steam copy?

Thank you again for your quick help.

isaporta  I would definitely uninstall the Steam copy if you're not using it.  Once you do that, if C&D still doesn't load, delete the EP04 folder here:

D:\The Sims 4

and download the pack again.  To delete the folder, you'll need to make sure the EA App is closed and the EABackgroundService is NOT running in the Task Manager's background processes list.  I would also clear the EA App's cache before reinstalling the pack.

https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/